Take time to get a flu vaccine.

• CDC recommends a yearly flu vaccine as the first and most important step in protecting against flu viruses.
• Flu vaccines help to reduce the burden of flu illnesses, hospitalizations and deaths on the health care system each year.
• This season, all flu vaccines will be designed to protect against the four flu viruses that research indicates will be most common.
• Everyone 6 months and older should get an annual flu vaccine, ideally by the end of October.
• Vaccination of people at higher risk of developing serious flu complications is especially important to decrease their risk of severe flu illness.
• People at higher risk of serious flu complications include young children, pregnant people, people with certain chronic health conditions like asthma, diabetes or heart and lung disease, and people 65 years and older.
• Vaccination also is important for health care workers, and other people who live with or care for people at higher risk to keep from spreading flu to them. This is especially true for people who work in long-term care facilities, which are home to many of the people most vulnerable to flu.
• Children younger than 6 months are at higher risk of serious flu illness but are too young to be vaccinated. People who care for infants should be vaccinated instead.

Take everyday preventive actions to stop the spread of germs.

• Take everyday preventive actions that are recommended to reduce the spread of flu.
  • Avoid close contact with people who are sick.
  • If you are sick, limit contact with others as much as possible to keep from infecting them.
• Cover coughs and sneezes.
  • Cover your nose and mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it.
• Wash your hands often with soap and water. If soap and water are not available, use an alcohol-based hand rub.
• Avoid touching your eyes, nose, and mouth. Germs spread this way.
• Clean and disinfect surfaces and objects that may be contaminated with viruses that cause flu.
• For flu, CDC recommends that people stay home for at least 24 hours after their fever is gone except to get medical care or other necessities. Fever should be gone without the need to use a fever-reducing medicine. Note that the stay-at-home guidance for COVID-19 may be different.

Take flu antiviral drugs if your doctor prescribes them.

• If you are sick with flu, antiviral drugs can be used to treat your illness.
• Antiviral drugs are different from antibiotics. They are prescription medicines (pills, liquid or an inhaled powder) and are not available over-the-counter.
• Flu antiviral drugs can make flu illness milder and shorten the time you are sick. They may also prevent serious flu complications. For people with higher risk factors, treatment with an antiviral drug can mean the difference between having a milder illness versus a very serious illness that could result in a hospital stay.
• Studies show that flu antiviral drugs work best for treatment when they are started within 2 days of getting sick, but starting them later can still be helpful, especially if the sick person has a higher risk factor or is very sick from flu.
• If you are at higher risk from flu and get flu symptoms, call your health care provider early so you can be treated with flu antivirals if needed. Follow your doctor’s instructions for taking this drug.

Flu symptoms include fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills and fatigue. Some people also may have vomiting and diarrhea. People may be infected with flu and have respiratory symptoms without a fever.

Flu Vaccination

Why should people get vaccinated against flu?

Influenza (flu) is a potentially serious disease that can lead to hospitalization and sometimes even death. Every flu season is different, and flu can affect people differently, but during typical flu seasons, millions of people get flu every year, hundreds of thousands of people are hospitalized and thousands to tens of thousands of people die from flu-related causes. Flu can mean a few days of feeling bad and missing work, school, or family events, or it can result in more serious illness. Complications of flu can include bacterial pneumonia, ear infections, sinus infections and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes. An annual seasonal flu vaccine is the best way to help reduce the risk of getting flu and any of its potentially serious complications. Vaccination has been shown to have many benefits including reducing the risk of flu illnesses, hospitalizations and even the risk of flu-related death. While some people who get a flu vaccine may still get sick with influenza, flu vaccination has been shown in several studies to reduce severity of illness.

How do flu vaccines work?

Flu vaccines cause antibodies to develop in the body about two weeks after vaccination. These antibodies provide protection against flu illness.

Seasonal flu vaccines are designed to protect against the influenza viruses that research indicates will be most common during the upcoming season. All flu vaccines in the United States are “quadrivalent” vaccines, which means they protect against four different flu viruses: an influenza A(H1N1) virus, an influenza A(H3N2) virus, and two influenza B viruses.

Flu Vaccine Options

For people younger than 65 years, CDC does not preferentially recommend any licensed, age-appropriate influenza (flu) vaccine over another during the 2022-2023 flu season. Options for this age group include inactivated influenza vaccine [IIV], recombinant influenza vaccine [RIV], or live attenuated influenza vaccine (LAIV), with no preference for any flu vaccine over another.

New for this season: For people 65 years and older, there are three flu vaccines that are preferentially recommended over standard-dose, unadjuvanted flu vaccines. These are Fluzone High-Dose Quadrivalent vaccine, Flublok Quadrivalent recombinant flu vaccine and Fluad Quadrivalent adjuvanted flu vaccine. More information is available at Flu & People 65 Years and Older.

All flu vaccines for the 2022-2023 season are quadrivalent vaccines, designed to protect against four different flu viruses, including two influenza A viruses and two influenza B viruses. Different vaccines are licensed for use in different age groups, and some vaccines are not recommended for some groups of people.

Available flu vaccines include:

• Standard-dose flu shots that are manufactured using virus grown in eggs. Several different brands of standard dose flu shots are available, including Afluria Quadrivalent, Fluarix Quadrivalent, FluLaval Quadrivalent, and Fluzone Quadrivalent. These vaccines are approved for use in children as young as 6 months. Most flu shots are given in the arm (muscle) with a needle. Afluria Quadrivalent can be given either with a needle (for people 6 months and older) or with a jet injector (for people 18 through 64 years only).
• A cell-based flu shot (Flucelvax Quadrivalent) containing virus grown in cell culture, which is approved for people 6 months and older. This vaccine is completely egg-free.
• A recombinant flu shot (Flublok Quadrivalent) which is a completely egg-free flu shot that is made using recombinant technology and is approved for use in people 18 years and older. This shot is made without flu viruses and contains three times the antigen (the part of the vaccine that helps your body build up protection against flu viruses) than other standard-dose inactivated flu vaccines, to help create a stronger immune response.
• An egg-based high dose flu shot (Fluzone High-Dose Quadrivalent), which is approved for use in people 65 years and older. This vaccine contains four times the antigen (the part of the vaccine that helps your body build up protection against flu viruses) than other standard-dose inactivated flu vaccines, to help create a stronger immune response.
• An egg-based adjuvanted flu shot (Fluad Quadrivalent), which is approved for people 65 years and older. This vaccine is made with an adjuvant (an ingredient that helps create a stronger immune response).
• An egg-based live attenuated flu nasal spray vaccine (FluMist Quadrivalent) made with attenuated (weakened) live flu viruses, which is approved for use in people 2 years through 49 years. This vaccine is not recommended for use in pregnant people, immunocompromised people, or people with certain medical conditions.

Are any of the available flu vaccines recommended over others?

Yes, for some people. For the 2022-2023 flu season, there are three flu vaccines that are preferentially recommended for people 65 years and older. These are Fluzone High-Dose Quadrivalent vaccine, Flublok Quadrivalent recombinant  flu vaccine and Fluad Quadrivalent adjuvanted flu vaccine. This recommendation was based on a review of available studies which suggests that, in this age group, these vaccines are potentially more effective than standard dose unadjuvanted flu vaccines. There is no preferential recommendation for people younger than 65 years.

What if a preferentially recommended flu vaccine is not available?

If none of the three flu vaccines preferentially recommended for people 65 years and older is available at the time of administration, people in this age group should get any other age-appropriate flu vaccine instead.

Who Should Be Vaccinated?

Everyone 6 months and older in the United States should get an influenza (flu) vaccine every season with rare exception. CDC’s Advisory Committee on Immunization Practices has made this “universal” recommendation since the 2010-2011 flu season.

Vaccination to prevent flu and its potentially serious complications is particularly important for people who are at higher risk of developing serious flu complications. A full list of age and health factors that confer increased risk is available at People at Higher Risk of Developing Flu-Related Complications.

Who Should Not Be Vaccinated?

Different influenza (flu) vaccines are approved for use in people in different age groups. In addition, some vaccines are not recommended for certain groups of people. Factors that can determine a person’s suitability for vaccination, or vaccination with a particular vaccine, include a person’s age, health (current and past) and any allergies to flu vaccine or its components.

When should I get vaccinated?

For most people who need only one dose of flu vaccine for the season, September and October are generally good times to be vaccinated against flu. Ideally, everyone should be vaccinated by the end of October. Additional considerations concerning the timing of vaccination for certain groups of people include:

• Most adults, especially those 65 years and older, and pregnant people in the first or second trimester should generally not get vaccinated early (in July or August) because protection may decrease over time. However, early vaccination can be considered for any person who is unable to return at a later time to be vaccinated.
• Some children need two doses of flu vaccine. For those children it is recommended to get the first dose as soon as vaccine is available, because the second dose needs to be given at least four weeks after the first. Vaccination during July and August also can be considered for children who need only one dose.
• Vaccination during July and August also can be considered for people who are in the third trimester of pregnancy during those months, because this can help protect their infants for the first few months after birth (when they are too young to be vaccinated).

Where can I get a flu vaccine?

Flu vaccines are offered in many doctor’s offices and clinics. Even if you don’t have a regular doctor or nurse, you can get a flu vaccine somewhere else like a health department, pharmacy, urgent care clinic, college health center, and even in some schools and workplaces.

Why do I need a flu vaccine every year?

A flu vaccine is needed every year for two reasons. First, a person’s immune protection from vaccination declines over time, so an annual flu vaccine is needed for optimal protection. Second, because flu viruses are constantly changing, the composition of flu vaccines is reviewed annually, and vaccines are updated to protect against the viruses that research indicates will be most common during the upcoming flu season. For the best protection, everyone 6 months and older should get vaccinated annually.

Does flu vaccine work right away?

No. It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against influenza virus infection. That’s why it’s best to get vaccinated before influenza viruses start to spread in your community.

Vaccine Effectiveness

Influenza (flu) vaccine effectiveness (VE) can vary. The protection provided by a flu vaccine varies from season to season and depends in part on the age and health status of the person getting the vaccine and the similarity or “match” between the viruses in the vaccine and those in circulation. During years when the flu vaccine match is good, it is possible to measure substantial benefits from flu vaccination in terms of preventing flu illness and complications. However, the benefits of flu vaccination will still vary, depending on characteristics of the person being vaccinated (for example, their health and age), what flu viruses are circulating that season and, potentially, which type of flu vaccine was used. More information is available at Vaccine Effectiveness – How well does the Flu Vaccine Work.

Can I get seasonal flu even though I got a flu vaccine this year?

Yes. It’s possible to get sick with flu even if you have been vaccinated (although you won’t know for sure unless you get a flu test). This is possible for the following reasons:

• You may be exposed to a flu virus shortly before getting vaccinated or during the period that it takes the body to gain protection after getting vaccinated. This exposure may result in you becoming ill with flu before the vaccine begins to protect you. (Antibodies that provide protection develop in the body about 2 weeks after vaccination.)
• You may be exposed to a flu virus that is not included in the seasonal flu vaccine. There are many different flu viruses that circulate every year. A flu vaccine is made to protect against the four flu viruses that research suggests will be most common.
• Unfortunately, some people can become infected with a flu virus that the vaccine is designed to protect against, despite getting vaccinated. Protection provided by flu vaccination can vary widely, based in part on health and age factors of the person getting vaccinated. In general, a flu vaccine works best among healthy younger adults and older children. Some older people and some people with certain chronic illnesses may develop less immunity after vaccination. Flu vaccination is not a perfect tool, but it is the best way to protect against flu virus infection.

What protection does a flu vaccine provide if I do get sick with flu?

Some people who get vaccinated may still get sick with flu. However, flu vaccination has been shown in studies to reduce severity of illness in people who get vaccinated but still get sick. A 2021 study showed that among adults, flu vaccination was associated with a 26% lower risk of ICU admission and a 31% lower risk of death from flu compared with those who were unvaccinated. A 2017 study showed that flu vaccination reduced deaths, intensive care unit (ICU) admissions, ICU length of stay, and overall duration of hospitalization among hospitalized adults with flu.

Vaccine Benefits

What are the benefits of flu vaccination?

There are many reasons to get an influenza (flu) vaccine each year.

Below is a summary of the benefits of flu vaccination and selected scientific studies that support these benefits.

• Flu vaccination can keep you from getting sick with flu.
  • Flu vaccine prevents millions of illnesses and flu-related doctor’s visits each year. For example, during 2019-2020, the last flu season prior to the COVID-19 pandemic, flu vaccination prevented an estimated 7.5 million influenza illnesses, 3.7 million influenza-associated medical visits, 105,000 influenza-associated hospitalizations, and 6,300 influenza-associated deaths.
  • During seasons when flu vaccine viruses are similar to circulating flu viruses, flu vaccine has been shown to reduce the risk of having to go to the doctor with flu by 40% to 60%.
• Flu vaccination has been shown in several studies to reduce severity of illness in people who get vaccinated but still get sick.
  • A 2021 study showed that among adults hospitalized with flu, vaccinated patients had a 26% lower risk of intensive care unit (ICU) admission and a 31% lower risk of death from flu compared with those who were unvaccinated.
  • A 2018 study showed that among adults hospitalized with flu, vaccinated patients were 59% less likely to be admitted to the ICU than those who had not been vaccinated. Among adults in the ICU with flu, vaccinated patients on average spent four fewer days in the hospital than those who were not vaccinated.
• Flu vaccination can reduce the risk of flu-associated hospitalization.
  • Flu vaccine prevents tens of thousands of hospitalizations each year. For example, during 2019-2020 flu vaccination prevented an estimated 105,000 flu-related hospitalizations.
  • A 2018 study showed that from 2012 to 2015, flu vaccination among adults reduced the risk of being admitted to an ICU with flu by 82%.
  • A 2017 study found that during 2009-2016, flu vaccines reduced the risk of flu-associated hospitalization among older adults by about 40% on average.
  • A 2014 study showed that flu vaccination reduced children’s risk of flu-related pediatric intensive care unit (PICU) admission by 74% during flu seasons from 2010-2012.
• Flu vaccination is an important preventive tool for people with certain chronic health conditions.
  • Flu vaccination has been associated with lower rates of some cardiac events among people with heart disease, especially among those who have had a cardiac event in the past year.
  • Flu vaccination can reduce the risk of a flu-related worsening of chronic lung disease (for example, chronic obstructive pulmonary disease (COPD) requiring hospitalization).
  • Among people with diabetes and chronic lung disease, flu vaccination has been shown in separate studies to be associated with reduced hospitalizations from a worsening of their chronic condition.
• Flu vaccination during pregnancy helps protect pregnant people from flu during and after pregnancy and helps protect their infants from flu in their first few months of life.
  • Vaccination reduces the risk of flu-associated acute respiratory infection in pregnant people by about one-half.
  • A 2018 study showed that getting a flu shot reduced a pregnant person’s risk of being hospitalized with flu by an average of 40% from 2010-2016.
  • A number of studies have shown that in addition to helping to protect pregnant people from flu, a flu vaccine given during pregnancy helps protect the baby from flu for several months after birth, when babies are too young to be vaccinated.
• Flu vaccine can be lifesaving in children.
  • A 2022 study showed that flu vaccination reduced children’s risk of severe life-threatening influenza by 75%.
  • A 2020 study found that during the 2018-2019 flu season, flu vaccination reduced flu-related hospitalization by 41% and flu-related emergency department visits by half among children (aged 6 months to 17 years old).
  • A 2017 study was the first of its kind to show that flu vaccination can significantly reduce children’s risk of dying from flu.
• Getting vaccinated yourself may also protect people around you, including those who are more vulnerable to serious flu illness, like babies and young children, older people, and people with certain chronic health conditions.

Despite the many benefits offered by flu vaccination, only about half of Americans get an annual flu vaccine. During an average flu season, flu can cause millions of illnesses, hundreds of thousands of hospitalizations and tens of thousands of deaths. Many more people could be protected from flu if more people got vaccinated.

Vaccine Match

What is meant by a “good match” between viruses in the vaccine and circulating influenza viruses?

A “good match” is said to occur when the flu vaccine viruses used to produce flu vaccine and the viruses circulating among people during a given flu season are “like” one another such that the antibodies induced by vaccination protect against infection caused by circulating viruses.

What if circulating flu viruses are different from vaccine viruses?

During seasons when one or more of the circulating viruses are different or “drifted” from the vaccine viruses, vaccine effectiveness against the drifted viruses can be reduced. It’s important to remember that flu vaccine protects against four different flu viruses and multiple different viruses usually circulate during any one season. Even if the effectiveness of the vaccine is reduced against one virus, vaccination can still be effective at preventing flu illness caused by the other circulating viruses. For these reasons, CDC continues to recommend flu vaccination for everyone 6 months and older even if vaccine effectiveness against one or more viruses is reduced.

Why is there sometimes not a good match between a vaccine virus and circulating viruses?

Flu viruses are constantly changing (called “antigenic drift”) – they can change from one season to the next or they can even change within the course of one flu season. Experts must pick which viruses to include in the vaccine many months in advance in order for vaccine to be produced and delivered on time. (For more information about the vaccine virus selection process visit Selecting the Viruses in the Influenza (Flu) Vaccine.) Because of these factors, there is always the possibility of a less than optimal match between circulating viruses and the viruses used to produce vaccine.

The production process for some seasonal vaccines also may impact how well vaccine works against certain viruses, especially influenza A(H3N2) viruses. Growth in eggs is part of the production process for many seasonal flu vaccines. While all influenza viruses undergo changes when they are grown in eggs, changes in influenza A(H3N2) viruses are more likely to result in antigenic changes compared with changes in other influenza viruses. These so-called “egg-adapted changes” are present in most of the vaccine viruses recommended for use in egg-based vaccine production and may reduce their effectiveness against circulating influenza viruses. Advances in vaccine production technologies (for example, cell-based and recombinant technology) and advanced molecular techniques are being explored as ways to improve flu vaccine effectiveness. Learn more by visiting, Advancements in Influenza Vaccines.

Will this season’s vaccine be a good match for circulating viruses?

It’s not possible to predict with certainty if a flu vaccine will be like circulating flu viruses because flu viruses are constantly changing. A flu vaccine is made to protect against the flu viruses that research and surveillance indicate will likely be most common during the upcoming season. Over the course of the flu season, CDC studies samples of circulating flu viruses to evaluate how close a match there is between viruses used to make the flu vaccine and circulating flu viruses. More information about the 2022-2023 flu season and recommended vaccines is available.

Vaccine Side Effects (What to Expect)

Can a flu vaccine give me flu?

No, a flu vaccine cannot cause flu illness. Flu vaccines that are given with a needle (flu shots) are currently made in two ways: the vaccine is made either with a) flu vaccine viruses that have been killed (inactivated) and are therefore not infectious, or b) with proteins from a flu virus (which is the case for recombinant influenza vaccine). Nasal spray vaccine is made with weakened (attenuated) live flu viruses and also cannot cause flu illness. The weakened viruses are cold-adapted, which means they are designed to only reproduce at the cooler temperatures found within the nose. The viruses cannot reproduce in the lungs or other areas where warmer temperatures exist.

What side effects can occur after getting a flu vaccine?

While a flu vaccine cannot give you flu illness, there are different side effects that may be associated with getting a flu shot or a nasal spray flu vaccine. These side effects are usually mild and short-lasting, especially when compared to symptoms of flu.

A flu shot: The viruses in a flu shot are killed (inactivated), so you cannot get flu from a flu shot. Some minor side effects that may occur are:

• Soreness, redness, and/or swelling where the shot was given
• Headache (low grade)
• Fever
• Muscle aches
• Nausea
• Fatigue

The nasal spray: The viruses in the nasal spray vaccine are weakened and do not cause influenza illness. In children, side effects from the nasal spray may include:

• Runny nose
• Wheezing
• Headache
• Vomiting
• Muscle aches
• Fever (low grade)

In adults, side effects from the nasal spray vaccine may include:

• Runny nose
• Headache
• Sore throat
• Cough

If these problems occur, they begin soon after vaccination and usually are mild and short-lived. A flu shot, like other injections, can occasionally cause fainting. Tell your provider if you feel dizzy or have vision changes or ringing in the ears. As with any medicine, there is a very remote chance of a vaccine causing a severe allergic reaction, other serious injury, or death. People who think that they have been injured by a flu vaccine can file a report with the Vaccine Adverse Event Reporting System (VAERS).

Vaccine Supply and Distribution

How much influenza vaccine is projected to be available for the 2022-2023 influenza season?

Flu vaccine is produced by private manufacturers, so supply depends on manufacturers. Vaccine manufacturers have projected that they will supply the United States with as many as 173.5 million to 183.5 million doses of influenza vaccines for the 2022-2023 season. These projections may change as the season progresses. All flu vaccines for the 2022-2023 season will be quadrivalent (four component). Most will be thimerosal-free or thimerosal-reduced vaccine (93%), and about 20% of flu vaccines will be egg-free.

Special Consideration Regarding Egg Allergy

People with egg allergies can receive any licensed, recommended age-appropriate influenza (flu) vaccine (IIV4, RIV4, ccIIV4, or LAIV4) that is otherwise appropriate. People who have a history of severe egg allergy (those who have had any symptom other than hives after exposure to egg) should be vaccinated in a medical setting, supervised by a health care provider who is able to recognize and manage severe allergic reactions. Two completely egg-free flu vaccine options are available: Flublok Quadrivalent recombinant flu vaccine and Flucelvax Quadrivalent cell-based flu shot.

For 2021-2022, CDC recommends use of any licensed, age-appropriate flu vaccine as an option for vaccination this season. These include:

• injectable flu vaccines, or flu shots. These include:
  • Flu shots that are made with inactivated viruses.
  • One flu shot that is made without influenza viruses.
• A live attenuated influenza vaccine, which is given by nasal spray.

Who should get a flu vaccine this season?

Everyone 6 months and older should get a flu vaccine every season with rare exceptions. Vaccination is particularly important for people who are at higher risk of serious complications from influenza.

Flu vaccination has important benefits. It can reduce flu illnesses, doctors’ visits, and missed work and school due to flu, as well as prevent flu-related hospitalizations and deaths.

Different flu vaccines are approved for use in different groups of people.

• There are flu shots approved for use in children as young as 6 months old and flu shots approved for use in adults 65 years and older.
• Flu shots also are recommended for pregnant people and people with certain chronic health conditions.
• The nasal spray flu vaccine is approved for use in non-pregnant people who are 2 years through 49 years of age. People who are pregnant and people with certain medical conditions should not receive the nasal spray flu vaccine.

There are many vaccine options to choose from. CDC does not recommend any one flu vaccine over another. The most important thing is for all people 6 months and older to get a flu vaccine every year.

If you have questions about which flu vaccine to get, talk to your doctor or other health care professional.

Who Should Not Receive a Flu Shot:

Most people should be vaccinated for influenza each year, But some people should not be vaccinated, or should not receive some types of influenza vaccines, depending upon things such as their age, health (current and past) and whether they have certain allergies.

Special Consideration Regarding Egg Allergy

People with egg allergies can receive any licensed, recommended age-appropriate influenza vaccine (IIV4, RIV4, or LAIV4) that is otherwise appropriate. People who have a history of severe egg allergy (those who have had any symptom other than hives after exposure to egg) should be vaccinated in a medical setting, supervised by a health care provider who is able to recognize and manage severe allergic reactions. Two completely egg-free (ovalbumin-free) flu vaccine options are available: quadrivalent recombinant vaccine and quadrivalent cell-based vaccine.

September and October are generally good times to be vaccinated against flu. Ideally, everyone should be vaccinated by the end of October. Additional considerations concerning the timing of vaccination for certain groups include:

• Adults, especially those 65 years and older, should generally not get vaccinated early (in July or August) because protection may decrease over time, but early vaccination can be considered for any person who is unable to return at a later time to be vaccinated.
• Children can get vaccinated as soon as vaccine becomes available, even if this is in July or August. Some children need two doses of flu vaccine. For those children it is recommended to get the first dose as soon as vaccine is available, because the second dose needs to given at least 4 weeks after the first.
• Early vaccination can also be considered for people who are in the third trimester of pregnancy, because this can help protect their infants during the first months of life (when they are too young to be vaccinated).

Get vaccinated before flu season starts

It takes about two weeks after vaccination for antibodies that protect against flu to develop in the body.

Everyone 6 months of age and older should get an influenza (flu) vaccine every season, with rare exceptions. Different influenza vaccines are approved for different age groups. Some people (for example, pregnant people and people with some chronic health conditions) should not get some types of influenza vaccines, and some people should not receive flu vaccines at all (though this is uncommon). Everyone who is vaccinated should receive a flu vaccine that is appropriate for their age and health status. For people younger than 65 years, there is no preference for any one vaccine over another. Beginning with the 2022-2023 flu season, there are three flu vaccines that are preferentially recommended for people aged 65 and older. These are Fluzone High-Dose Quadrivalent vaccine, Flublok Quadrivalent

All persons aged 6 months of age and older are recommended for annual flu vaccination, with rare exception.

Vaccination is particularly important for people who are at higher risk of developing serious flu complications.

Influenza (Flu) Shots

People who can get the flu shot:

Flu shots are appropriate for most people.

• Different flu shots are approved for people of different ages. Everyone should get a vaccine that is appropriate for their age.
• There are standard-dose inactivated flu vaccines that are approved for people as young as 6 months of age.
• Some vaccines are only approved for adults. For example, the recombinant flu vaccine is approved for people aged 18 years and older, and the adjuvanted and high-dose inactivated vaccines are approved for people 65 years and older.
• Pregnant people and people with certain chronic health conditions can get a flu shot.
• People with egg allergy can get a flu shot

People who SHOULD NOT get a flu shot include:

• Children younger than 6 months of age are too young to get a flu shot.
• People with severe, life-threatening allergies to any ingredient in a flu vaccine (other than egg proteins) should not get that vaccine. This might include gelatin, antibiotics, or other ingredients. .
• People who have had a severe allergic reaction to a dose of influenza vaccine should not get that flu vaccine again and might not be able to receive other influenza vaccines. If you have had a severe allergic reaction to an influenza vaccine in the past, it is important to talk with your health care provider to help determine whether vaccination is appropriate for you.

People who should talk to their health care provider before getting a flu shot:

If you have one of the following conditions, talk with your health care provider. He or she can help decide whether vaccination is right for you, and select the best vaccine for your situation:

• If you have an allergy to eggs or any of the ingredients in the vaccine. Talk to your doctor about your allergy.
• If you ever had Guillain-Barré Syndrome (a severe paralyzing illness, also called GBS). Some people with a history of GBS should not get a flu vaccine. Talk to your doctor about your GBS history.
• If you had a severe allergic reaction to a previous dose of any other flu vaccine, talk to your health care provider.
• If you are not feeling well, talk to your doctor about your symptoms.

Nasal Spray Flu Vaccine

People who can get a nasal spray flu vaccine:
The nasal spray vaccine is approved for people 2 years through 49 years of age. Many people in this age group can receive the nasal spray vaccine, including people with egg allergies. The nasal spray vaccine is not recommended for some groups.

People who SHOULD NOT get a nasal spray vaccine:

• Children younger than 2 years of age.
• Adults 50 years of age and older.
• People who have had a severe or life-threatening allergic reaction to any ingredient in the nasal spray vaccine (other than egg proteins).
• People who have had a severe allergic reaction to any flu vaccine.
• Children and adolescents 2 through 17 years of age who are receiving aspirin- or salicylate-containing medications.
• People with weakened immune systems (immunosuppression) due to any cause, including (but not limited to) immunosuppression from medications, congenital or acquired immune disorders, HIV infection, or asplenia.
• People who care for or are close contacts of severely immunocompromised persons who require a protected environment (or otherwise avoid contact with those persons for 7 days after getting the nasal spray vaccine).
• Pregnant people.
• Children 2 years through 4 years who have asthma or who have had a history of wheezing in the past 12 months.
• People with cerebrospinal fluid (CSF) leaks (communication and leakage of fluid between the space surrounding the brain and the nose, throat, ear, or any other place in the head).
• People with cochlear implants.
• People who have recently taken influenza antiviral drugs. This depends on the specific influenza antiviral medication that was taken, and how recently the last dose was taken.

People who should talk to their health care provider before getting a nasal spray vaccine:

If you have one of the following conditions, talk with your health care provider. He or she can help decide whether vaccination is right for you, and select the best vaccine for your situation:

• People with asthma 5 years and older.
• People with other underlying medical conditions that can put them at higher risk of developing serious flu complications. These include conditions such as chronic lung diseases, heart disease (except isolated hypertension), kidney disease, liver disorders, neurologic and neuromuscular disorders, blood disorders, or metabolic disorders (such as diabetes).
• People with moderate or severe acute illness with or without fever.
• People with Guillain-Barré Syndrome after a previous dose of influenza vaccine.

Who Should be Prioritized for Flu Vaccination During a Vaccine Shortage

When vaccine supply is limited, vaccination efforts should focus on delivering vaccination to the following people (no hierarchy is implied by order of listing):

• Children aged 6 months through 4 years (59 months);
• People aged 50 years and older;*
• People with chronic pulmonary (including asthma) or cardiovascular (except isolated hypertension), renal, hepatic, neurologic, hematologic, or metabolic disorders (including diabetes mellitus);
• People who are immunosuppressed due to any cause, including immunosuppression caused by medications or by human immunodeficiency virus (HIV) infection;
• People who are or will be pregnant during the influenza season and people up to two weeks after delivery;
• People who are aged 6 months through 18 years who are receiving aspirin or salicylate-containing medications and who might be at risk for experiencing Reye syndrome after influenza virus infection;
• People who are residents of nursing homes and other long-term care facilities;
• American Indian or Alaska Native persons;
• People with extreme obesity (body-mass index [BMI] is 40 or greater);
• Health care personnel;
• Household contacts and caregivers of children under 5 years and adults aged 50 years and older; and
• Household contacts and caregivers of people with medical conditions that put them at increased risk for severe illness and complications from influenza.

*Among adults, complications, hospitalizations, and deaths due to influenza are generally most common among people 65 years and older. However, adults 50 years and older are a priority group for vaccination because they may be more likely to have chronic medical conditions that put them at higher risk of severe influenza illness.

People with egg allergies can receive any licensed, recommended age-appropriate influenza (flu) vaccine (IIV4, RIV4, ccIIV4, or LAIV4) that is otherwise appropriate. People who have a history of severe egg allergy (those who have had any symptom other than hives after exposure to egg) should be vaccinated in a medical setting, supervised by a health care provider who is able to recognize and manage severe allergic reactions. Two completely egg-free flu vaccine options are available: Flublok Quadrivalent recombinant flu vaccine and Flucelvax Quadrivalent cell-based flu shot.

There are many reasons to get an influenza (flu) vaccine each year.

Below is a summary of the benefits of flu vaccination and selected scientific studies that support these benefits.

• Flu vaccination can keep you from getting sick with flu.
  • Flu vaccine prevents millions of illnesses and flu-related doctor’s visits each year. For example, during 2019-2020, the last flu season prior to the COVID-19 pandemic, flu vaccination prevented an estimated 7.5 million influenza illnesses, 3.7 million influenza-associated medical visits, 105,000 influenza-associated hospitalizations, and 6,300 influenza-associated deaths.
  • During seasons when flu vaccine viruses are similar to circulating flu viruses, flu vaccine has been shown to reduce the risk of having to go to the doctor with flu by 40% to 60%.
• Flu vaccination has been shown in several studies to reduce severity of illness in people who get vaccinated but still get sick.
  • A 2021 study showed that among adults hospitalized with flu, vaccinated patients had a 26% lower risk of intensive care unit (ICU) admission and a 31% lower risk of death from flu compared with those who were unvaccinated.
  • A 2018 study showed that among adults hospitalized with flu, vaccinated patients were 59% less likely to be admitted to the ICU than those who had not been vaccinated. Among adults in the ICU with flu, vaccinated patients on average spent four fewer days in the hospital than those who were not vaccinated.
• Flu vaccination can reduce the risk of flu-associated hospitalization.
  • Flu vaccine prevents tens of thousands of hospitalizations each year. For example, during 2019-2020 flu vaccination prevented an estimated 105,000 flu-related hospitalizations.
  • A 2018 study showed that from 2012 to 2015, flu vaccination among adults reduced the risk of being admitted to an ICU with flu by 82%.
  • A 2017 study found that during 2009-2016, flu vaccines reduced the risk of flu-associated hospitalization among older adults by about 40% on average.
  • A 2014 study showed that flu vaccination reduced children’s risk of flu-related pediatric intensive care unit (PICU) admission by 74% during flu seasons from 2010-2012.
• Flu vaccination is an important preventive tool for people with certain chronic health conditions.
  • Flu vaccination has been associated with lower rates of some cardiac events among people with heart disease, especially among those who have had a cardiac event in the past year.
  • Flu vaccination can reduce the risk of a flu-related worsening of chronic lung disease (for example, chronic obstructive pulmonary disease (COPD) requiring hospitalization).
  • Among people with diabetes and chronic lung disease, flu vaccination has been shown in separate studies to be associated with reduced hospitalizations from a worsening of their chronic condition.
• Flu vaccination during pregnancy helps protect pregnant people from flu during and after pregnancy and helps protect their infants from flu in their first few months of life.
  • Vaccination reduces the risk of flu-associated acute respiratory infection in pregnant people by about one-half.
  • A 2018 study showed that getting a flu shot reduced a pregnant person’s risk of being hospitalized with flu by an average of 40% from 2010-2016.
  • A number of studies have shown that in addition to helping to protect pregnant people from flu, a flu vaccine given during pregnancy helps protect the baby from flu for several months after birth, when babies are too young to be vaccinated.
• Flu vaccine can be lifesaving in children.
  • A 2022 study showed that flu vaccination reduced children’s risk of severe life-threatening influenza by 75%.
  • A 2020 study found that during the 2018-2019 flu season, flu vaccination reduced flu-related hospitalization by 41% and flu-related emergency department visits by half among children (aged 6 months to 17 years old).
  • A 2017 study was the first of its kind to show that flu vaccination can significantly reduce children’s risk of dying from flu.
• Getting vaccinated yourself may also protect people around you, including those who are more vulnerable to serious flu illness, like babies and young children, older people, and people with certain chronic health conditions.

Despite the many benefits offered by flu vaccination, only about half of Americans get an annual flu vaccine. During an average flu season, flu can cause millions of illnesses, hundreds of thousands of hospitalizations and tens of thousands of deaths. Many more people could be protected from flu if more people got vaccinated.

Influenza (flu) vaccines cause antibodies to develop in the body about two weeks after vaccination. These antibodies provide protection against infection with the flu viruses that are used to make vaccine. The seasonal flu vaccine protects against the influenza viruses that research suggests will be most common during the upcoming season.

Flu Shot

Flu shots are vaccines given with a needle, usually in the arm.

Quadrivalent Flu Vaccine

Quadrivalent flu vaccines protect against four different flu viruses.

High-Dose Flu Vaccine

The high dose vaccine (Fluzone High-Dose Quadrivalent) contains four times the amount of antigen (the part of the vaccine that helps your body build up protection against flu viruses) as a regular flu shot to help create a stronger immune response. It is approved for use in people 65 years and older.

Cell-Based Flu Vaccines

Cell-based vaccines (Flucelvax Quadrivalent) are grown in mammal cell culture instead of in hens' eggs. This vaccine is completely egg-free and is approved for people 6 months and older.

Flu Vaccination by Jet Injector

Flu vaccination via jet injector (Afluria Quadrivalent) is approved for use in people 18 through 64 years old.

Nasal Spray Flu Vaccine

Live Attenuated Influenza Vaccine [LAIV] (FluMist Quadrivalent) is given as a nasal spray. This vaccine is made with attenuated (weakened) live flu viruses, and is approved for use in people aged 2 through 49 years. This vaccine is not recommended for use in pregnant people, immunocompromised people, or people with certain medical conditions.

Adjuvanted Flu Vaccine

Adjuvanted flu vaccine (Fluad Quadrivalent vaccine) is made with an ingredient (an adjuvant) that helps create a stronger immune response and is licensed specifically for people 65 years and older.

Recombinant Flu Vaccine

Recombinant flu vaccines (Flublok Quadrivalent) are produced using a method that does not require an egg-grown vaccine virus. This vaccine contains three times the antigen (the part of the vaccine that helps your body build up protection against flu viruses) than other standard-dose inactivated flu vaccines, to help create a stronger immune response.

You can get a flu vaccine and a COVID-19 vaccine at the same visit if you are due for both vaccines. This is an option.

What is coadministration?

Coadministration of vaccines refers to giving or getting more than one vaccine during a visit. This is common clinical practice. While there are some exceptions, many vaccines can be given at the same visit.

Why would a health care provider encourage people to get both vaccines at the same time?

Giving more than one vaccine at a visit, also called “coadministration” is common medical practice and is recommended. The idea is to get people up to date on all the vaccines they are due for at one visit. This can ensure that people get all of their vaccines, in case they are not able to return visit for additional vaccinations at a later time.

Can flu vaccines and COVID-19 vaccines be coadministered?

Yes, flu vaccines and COVID-19 vaccines can be given at the same visit if you are due for both vaccines.

Is it safe to get a flu vaccine and a COVID-19 vaccine at the same time?

Studies conducted throughout the COVID-19 pandemic indicate that it is safe to get both a flu vaccine and a COVID-19 vaccine at the same visit. A CDC study published this summer showed people who got a flu vaccine and an mRNA COVID-19 booster vaccine at the same time were slightly more likely (8% to 11%) to have reactions including fatigue, headache, and muscle ache than people who only got a COVID-19 mRNA booster vaccine, but these reactions were mostly mild and went away quickly. The findings of this study are consistent with safety data from clinical trials that did not find any safety concerns with giving both vaccines at the same time.

Why should I get a flu vaccine and a COVID-19 vaccine at the same visit?

Getting both vaccines at the same time if you are due for both is an option for consumers. Some people might prefer to get their vaccines at one time. This might be more convenient than having two separate visits.

If I get both vaccines at the same visit, where should I get them?

CDC has guidance for health care providers on giving more than one vaccine at the same visit. For flu and COVID-19 vaccines, you can either get both vaccines in the same arm (at least an inch apart), or you can get them in different arms. Either is okay. The high-dose (Fluzone High-Dose Quadrivalent) or adjuvanted flu vaccine (Fluad Quadrivalent) may be more likely to cause side effects compared to standard dose flu vaccines. You may want to get these high-dose flu vaccines in different arms than the arm receiving a COVID-19 vaccine to reduce side effects in one arm.

If I decide to wait between getting my flu vaccine and a COVID-19 vaccine, is there a recommended waiting time between vaccines?

No, there’s no recommended waiting time between getting a flu vaccine and a COVID-19 vaccine.

For the United States there are three different flu vaccine production technologies approved by the U.S. Food and Drug Administration (FDA):

• egg-based flu vaccine,
• cell culture-based flu vaccine, and
• recombinant flu vaccine.

All commercially available flu vaccines in the United States are made by private sector manufacturers. Different manufacturers use different production technologies, but all flu vaccines meet FDA safety and effectiveness requirements. Different vaccines have different indications.

Egg-Based Flu Vaccines

The most common way that flu vaccines are made is using an egg-based manufacturing process

that has been used for more than 70 years. Egg-based vaccine manufacturing is used to make both inactivated (killed) vaccine (usually called the “flu shot”) and live attenuated (weakened virus) vaccine (usually called the “nasal spray flu vaccine”).

The egg-based production process begins with CDC or another laboratory partner in the WHO Global Influenza Surveillance and Response System providing private sector manufacturers with candidate vaccine viruses (CVVs) grown in chicken eggs per current FDA regulatory requirements. These CVVs are then injected into fertilized chicken eggs and incubated for several days to allow the viruses to replicate. The fluid containing virus is harvested from the eggs. For inactivated influenza vaccines (i.e., flu shots), the vaccine viruses are then inactivated (killed), and the virus antigen is purified. The manufacturing process continues with quality testing, packaging and distribution. For the nasal spray flu vaccine (i.e., the live attenuated influenza vaccine – LAIV), the starting CVVs are used to make live, but weakened viruses that are then used in vaccine production. FDA tests and approves all flu vaccines prior to release and shipment.

There are several different manufacturers that use egg-based production technology to make flu vaccines for use in the United States. This production method requires large numbers of chicken eggs to produce vaccine and may take longer than other production methods.

Cell Culture-Based Flu Vaccines

There also is a cell culture-based production process for flu vaccines that was approved by FDA in 2012. Originally, this production process also began with chicken egg-grown CVVs per FDA regulations. However, on August 31, 2016, FDA issued an approval for Seqirus, the sole FDA-approved cell culture-based flu vaccine manufacturer in the United States, to begin using cell culture-grown CVVs. Currently, cell culture-based manufacturing is used to make inactivated flu vaccines (e.g., flu shots), not LAIV (nasal spray flu vaccine).

The process of creating cell culture-based flu vaccines involves several steps. First, CDC or one of its laboratory partners, uses influenza viruses that have been grown in cultured mammalian cells to make CVVs, which are then provided to a vaccine manufacturer. Next, the vaccine manufacturer inoculates the CVVs into cultured mammalian cells (instead of into chicken eggs) and allows the CVVs to replicate (i.e., make copies) for a few days. Then, the virus-containing fluid is collected from the cells and the virus antigen is purified. The manufacturing process continues with purification, virus inactivation, and testing. Finally, FDA tests and approves the vaccines prior to release and shipment.

Cell culture-based flu vaccine production does not require chicken eggs because the vaccine viruses used to make vaccine are grown in mammalian cell cultures (no animals are harmed by this process). Cell culture-based technology also has the potential for a faster start-up of the flu vaccine manufacturing process.

While viruses used in previous seasons’ cell culture-based vaccine have been grown in cell cultures, prior to the 2019-2020 season, some of the viruses provided to the manufacturer had been first propagated in chicken eggs. Beginning with the 2021-2022 season, all four flu viruses used in the cell culture-based vaccine are grown in cell cultures only, making the vaccine completely egg-free.

Recombinant Flu Vaccines

This is a picture of an influenza virus. The virus’ hemagglutinin (HA) surface proteins are depicted in blue. The HAs of an influenza virus are antigens. Antigens are features of the influenza virus that are recognized by the immune system and that trigger a protective immune response. Most flu vaccines are designed to trigger an immune response against the HAs of circulating influenza viruses.

A third production technology for flu vaccines was approved for use in the U.S. market in 2013 and involves using recombinant technology. Recombinant flu vaccines do not require the use of a candidate vaccine virus (CVV) for production. Instead, recombinant vaccines are created synthetically. To make a recombinant vaccine, flu scientists first obtain the virus’ gene that contains the genetic instructions for making the HA. HA is an antigen, which is a feature of a flu virus that triggers the human immune system to create antibodies that specifically target the virus. This HA gene is then combined with a baculovirus, a virus that infects invertebrates. This results in a “recombinant” baculovirus. The role of the baculovirus is to help deliver the genetic instructions for making flu HA antigen into a host cell. Once the recombinant virus enters a Food and Drug Administration (FDA) qualified host cell line, it instructs the cells to rapidly produce the HA antigen. This antigen is grown in bulk, collected, purified, and then packaged as recombinant flu vaccine. Prior to FDA approval and release of the vaccine lots to the public, these vaccines are tested for quality and potency by FDA.

This production method does not require an egg-grown vaccine virus and does not use chicken eggs at any stage of the production process. While there are other vaccines that use similar recombinant manufacturing processes, only one flu vaccine is FDA approved for use in the United States at this time. This production process is the fastest because it bypasses the need for CVVs adapted for growth in eggs or the development of cell culture-based vaccine viruses.

CDC and FDA monitor the safety of all vaccines licensed in the United States, including seasonal flu vaccines.

Misconceptions about Flu Vaccines

Can a flu vaccine give you flu?

No, flu vaccines cannot cause flu illness. Flu vaccines given with a needle (i.e., flu shots) are made with either inactivated (killed) viruses, or with only a single protein from the flu virus. The nasal spray vaccine contains live viruses that are attenuated (weakened) so that they will not cause illness.

Are any of the available flu vaccines recommended over the others?

Yes, for some people. For the 2022-2023 flu season, there are three flu vaccines that are preferentially recommended for people 65 years and older. These are Fluzone High-Dose Quadrivalent vaccine, Flublok Quadrivalent recombinant  flu vaccine and Fluad Quadrivalent adjuvanted flu vaccine. This recommendation was based on a review of available studies which suggests that, in this age group, these vaccines are potentially more effective than standard dose unadjuvanted flu vaccines. There is no preferential recommendation for people younger than 65 years.

What if a preferentially recommended flu vaccine is not available?

If none of the three flu vaccines preferentially recommended for people 65 years and older is available at the time of administration, people in this age group should get any other age-appropriate flu vaccine instead.

Is it better to get sick with flu than to get a flu vaccine?

No. Flu can be a serious disease, particularly among young children, older adults, and people with certain chronic health conditions, such as asthma, heart disease or diabetes. Any flu infection can carry a risk of serious complications, hospitalization or death, even among otherwise healthy children and adults. Therefore, getting vaccinated is a safer choice than risking illness to obtain immune protection.

Do I really need a flu vaccine every year?

Yes. CDC recommends a yearly flu vaccine for everyone 6 months of age and older with rare exception. The reason for this is that a person’s immune protection from vaccination declines over time, so an annual vaccination is needed to get the “optimal” or best protection against the flu. Additionally, flu viruses are constantly changing, so the vaccine composition is reviewed each year and updated as needed.

Why do some people not feel well after getting a seasonal flu vaccine?

Some people report having mild side effects after flu vaccination. The most common side effects from flu shots are soreness, redness, tenderness or swelling where the shot was given. Low-grade fever, headache and muscle aches also may occur. If these reactions occur, they usually begin soon after vaccination and last 1-2 days.

Side effects from the nasal spray flu vaccine may include: runny nose, wheezing, headache, vomiting, muscle aches, fever, sore throat and cough. If these problems occur, they usually begin soon after vaccination and are mild and short-lived. The most common reactions people have to flu vaccines are considerably less severe than the symptoms caused by actual flu illness.

What about serious reactions to flu vaccine?

Serious allergic reactions to flu vaccines are very rare. If they do occur, it is usually within a few minutes to a few hours after vaccination. While these reactions can be life-threatening, effective treatments are available.

What about people who get a seasonal flu vaccine and still get sick with flu symptoms?

There are several reasons why someone might get flu symptoms even after they have been vaccinated against flu.

• Someone can get sick with another respiratory virus besides flu such as rhinoviruses or SARS-CoV-2 (the virus that causes COVID-19). Other respiratory viruses can cause symptoms similar to flu, and they can also spread and cause illness during flu season. Flu vaccines only protect against flu and its complications, not other illnesses.
• Someone can be exposed to flu viruses shortly before getting vaccinated or during the two-week period after vaccination that it takes the body to develop immune protection. This exposure may result in a person becoming sick with flu before protection from vaccination takes effect.
• Flu vaccines vary in how well they work, and someone can get vaccinated but still get sick with flu. There are many different flu viruses that spread and cause illness among people, so this can happen if someone is exposed to a flu virus that is very different from the viruses in the flu vaccine. The ability of a flu vaccine to protect a person depends partially on the similarity or “match” between the vaccine viruses chosen to make vaccine and those spreading and causing illness. Even when that happens though, flu vaccination can still reduce severity of illness.

Can vaccinating someone twice provide added immunity?

In adults, studies have not shown a benefit from getting more than one dose of vaccine during the same influenza season, even among elderly persons with weakened immune systems. Except for children getting vaccinated for the first time, only one dose of flu vaccine is recommended each season.

Is it true that getting a flu vaccine can make you more susceptible to other respiratory viruses?

Flu vaccines are not thought to make people more susceptible to other respiratory infections.

A 2012 study that suggested that flu vaccination might make people more susceptible to other respiratory infections. After that study was published, many experts looked into this issue further and conducted additional studies to see if the findings could be replicated. No other studies have found this effect. It’s not clear why this finding was detected in the one study, but the majority of evidence suggests that this is not a common or regular occurrence and that flu vaccination does not, in fact, make people more susceptible to other respiratory infections.

Does a flu vaccination increase your risk of getting COVID-19?

There is no evidence that getting a flu vaccination increases your risk of getting sick from a coronavirus, like the one that causes COVID-19.

You may have heard about a study published in January 2020 that reported an association between flu vaccination and risk of four commonly circulating seasonal coronaviruses, but not the one that causes COVID-19. This report was later found to be incorrect.

The results from that initial study led researchers in Canada to look at their data to see if they could find similar results in their population. The results from this study showed that flu vaccination did not increase risk for these seasonal coronaviruses. The Canadian findings highlighted the protective benefits of flu vaccination.

The Canadian researchers also identified a flaw in the methods of the first study, noting that it violated the part of study design that compares vaccination rates among patients with and without flu (test negative design). This flaw led to the incorrect association between flu vaccination and seasonal coronavirus risk. When these researchers reexamined data from the first study using correct methods, they found that flu vaccination did not increase risk for infection with other respiratory viruses, including seasonal coronaviruses.

Misconceptions about Flu Vaccine Effectiveness

Influenza (flu) vaccine effectiveness (VE) can vary. The protection provided by a flu vaccine varies from season to season and depends in part on the age and health status of the person getting the vaccine and the similarity or “match” between the viruses in the vaccine and those in circulation. During years when the flu vaccine match is good, it is possible to measure substantial benefits from flu vaccination in terms of preventing flu illness and complications. However, the benefits of flu vaccination will still vary, depending on characteristics of the person being vaccinated (for example, their health and age), what flu viruses are circulating that season and, potentially, which type of flu vaccine was used. More information is available at Vaccine Effectiveness – How well does the Flu Vaccine Work.

There are many reasons to get an influenza (flu) vaccine each year.

Below is a summary of the benefits of flu vaccination and selected scientific studies that support these benefits.

• Flu vaccination can keep you from getting sick with flu.
  • Flu vaccine prevents millions of illnesses and flu-related doctor’s visits each year. For example, during 2019-2020, the last flu season prior to the COVID-19 pandemic, flu vaccination prevented an estimated 7.5 million influenza illnesses, 3.7 million influenza-associated medical visits, 105,000 influenza-associated hospitalizations, and 6,300 influenza-associated deaths.
  • During seasons when flu vaccine viruses are similar to circulating flu viruses, flu vaccine has been shown to reduce the risk of having to go to the doctor with flu by 40% to 60%.
• Flu vaccination has been shown in several studies to reduce severity of illness in people who get vaccinated but still get sick.
  • A 2021 study showed that among adults hospitalized with flu, vaccinated patients had a 26% lower risk of intensive care unit (ICU) admission and a 31% lower risk of death from flu compared with those who were unvaccinated.
  • A 2018 study showed that among adults hospitalized with flu, vaccinated patients were 59% less likely to be admitted to the ICU than those who had not been vaccinated. Among adults in the ICU with flu, vaccinated patients on average spent four fewer days in the hospital than those who were not vaccinated.
• Flu vaccination can reduce the risk of flu-associated hospitalization.
  • Flu vaccine prevents tens of thousands of hospitalizations each year. For example, during 2019-2020 flu vaccination prevented an estimated 105,000 flu-related hospitalizations.
  • A 2018 study showed that from 2012 to 2015, flu vaccination among adults reduced the risk of being admitted to an ICU with flu by 82%.
  • A 2017 study found that during 2009-2016, flu vaccines reduced the risk of flu-associated hospitalization among older adults by about 40% on average.
  • A 2014 study showed that flu vaccination reduced children’s risk of flu-related pediatric intensive care unit (PICU) admission by 74% during flu seasons from 2010-2012.
• Flu vaccination is an important preventive tool for people with certain chronic health conditions.
  • Flu vaccination has been associated with lower rates of some cardiac events among people with heart disease, especially among those who have had a cardiac event in the past year.
  • Flu vaccination can reduce the risk of a flu-related worsening of chronic lung disease (for example, chronic obstructive pulmonary disease (COPD) requiring hospitalization).
  • Among people with diabetes and chronic lung disease, flu vaccination has been shown in separate studies to be associated with reduced hospitalizations from a worsening of their chronic condition.
• Flu vaccination during pregnancy helps protect pregnant people from flu during and after pregnancy and helps protect their infants from flu in their first few months of life.
  • Vaccination reduces the risk of flu-associated acute respiratory infection in pregnant people by about one-half.
  • A 2018 study showed that getting a flu shot reduced a pregnant person’s risk of being hospitalized with flu by an average of 40% from 2010-2016.
  • A number of studies have shown that in addition to helping to protect pregnant people from flu, a flu vaccine given during pregnancy helps protect the baby from flu for several months after birth, when babies are too young to be vaccinated.
• Flu vaccine can be lifesaving in children.
  • A 2022 study showed that flu vaccination reduced children’s risk of severe life-threatening influenza by 75%.
  • A 2020 study found that during the 2018-2019 flu season, flu vaccination reduced flu-related hospitalization by 41% and flu-related emergency department visits by half among children (aged 6 months to 17 years old).
  • A 2017 study was the first of its kind to show that flu vaccination can significantly reduce children’s risk of dying from flu.
• Getting vaccinated yourself may also protect people around you, including those who are more vulnerable to serious flu illness, like babies and young children, older people, and people with certain chronic health conditions.

Despite the many benefits offered by flu vaccination, only about half of Americans get an annual flu vaccine. During an average flu season, flu can cause millions of illnesses, hundreds of thousands of hospitalizations and tens of thousands of deaths. Many more people could be protected from flu if more people got vaccinated.

*References for the studies listed above can be found at Publications on Influenza Vaccine Benefits.

Misconceptions about the Timing of Seasonal Influenza Vaccination

Should I wait to get vaccinated so that my immunity lasts through the end of the season?

How long you are immune or your “duration of immunity” is discussed in the ACIP recommendations. While delaying getting of vaccine until later in the fall may lead to higher levels of immunity during winter months, this should be balanced against possible risks, such as missed opportunities to receive vaccine and difficulties associated with vaccinating a large number of people within a shorter time period.

Is it too late to get vaccinated after Thanksgiving (or the end of November)?

No. Vaccination can still be beneficial as long as flu viruses are circulating. If you have not been vaccinated by Thanksgiving (or the end of November), it can still be protective to get vaccinated in December or later. Flu is unpredictable and seasons can vary. Seasonal flu disease usually peaks between December and March most years, but disease can occur as late as May.

Misconceptions about Physician Consent for Vaccination

Do pregnant people or people with pre-existing medical conditions need special permission or written consent from their doctor to get a flu vaccine?

No. There is no recommendation for pregnant people or people with pre-existing medical conditions to seek special permission or secure written consent from their doctor for vaccination if they get vaccinated at a worksite clinic, pharmacy or other location outside of their physician’s office. With rare exception, CDC recommends an annual flu vaccine for everyone 6 months of age and older, including pregnant people and people with medical conditions.

A variety of flu vaccines are available (Table 1). Vaccine providers should be aware of the approved age indications of the vaccine they are using and of any contraindications or precautions. Providers also should appropriately screen all people getting vaccinated for allergies to vaccine components or other contraindications. People who have previously had a severe allergic reaction to influenza vaccine or any of its ingredients should generally not be vaccinated.

There are some people who should not get a flu vaccine without first speaking with their doctor. These include:

• People who have a moderate-to-severe illness with or without a fever (they should wait until they recover to get vaccinated), and
• People with a history of Guillain-Barré Syndrome (a severe paralytic illness, also called GBS) that occurred after receiving influenza vaccine and who are not at risk for severe illness from influenza should generally not receive vaccine. Tell your doctor if you ever had Guillain-Barré Syndrome. Your doctor will help you decide whether the vaccine is recommended for you.

Pregnant people or people with pre-existing medical conditions who get vaccinated should get a flu shot.

If a person is vaccinated by someone other than their primary health care provider, the vaccinating provider should ensure that the patient and, if possible, the patient’s medical provider have documentation of vaccination.

For a complete list of people who should not get a flu vaccine before speaking with their doctor, please review the influenza Vaccine Information Statement for the inactivated or recombinant flu vaccine or live, intranasal influenza vaccine.

Misconceptions about “Stomach Flu”

Is the “stomach flu” really flu?

No. Many people use the term “stomach flu” to describe illnesses with nausea, vomiting or diarrhea. These symptoms can be caused by many different viruses, bacteria or even parasites. While vomiting, diarrhea, and being nauseous or “sick to your stomach” can sometimes be related to flu — more commonly in children than adults — these problems are rarely the main symptoms of influenza. Flu is a respiratory disease and not a stomach or intestinal disease.

How effective are flu vaccines?

CDC conducts studies each year to determine how well influenza (flu) vaccines protect against flu. While vaccine effectiveness (VE) can vary, recent studies show that flu vaccination reduces the risk of flu illness by between 40% and 60% among the overall population during seasons when most circulating flu viruses are well-matched to those used to make flu vaccines. In general, current flu vaccines tend to work better against influenza B and influenza A(H1N1) viruses and offer lower protection against influenza A(H3N2) viruses. Go to “Does flu vaccine effectiveness vary by type or subtype?” and “Why is flu vaccine typically less effective against influenza A H3N2 viruses?” for more information.

What are factors that influence how well flu vaccines work?

How well flu vaccines work (or their ability to protect against a certain outcome) can vary from season to season. Protection can vary depending on who is being vaccinated. At least two factors play an important role in determining the likelihood that vaccination will protect a person from flu illness: 1) characteristics of the person being vaccinated (such as their age and health), and 2) how well the vaccines “match” the flu viruses spreading in the community. When flu vaccines are not well matched to one or more circulating influenza viruses, it is possible that vaccination may provide little or no protection from illness caused by those viruses, but still provide protection against other flu viruses that circulate during the season. When there is a good match between flu vaccines and circulating viruses, vaccination provides substantial benefits by preventing flu illness and complications.

Each flu season, researchers try to determine how well flu vaccines work as a public health intervention. Estimates of how well a flu vaccine works can vary based on study design, outcome(s) measured, population studied and type of flu vaccine. Differences between studies must be considered when results are compared.

What are the benefits of flu vaccination?

There are many reasons to get an influenza (flu) vaccine each year.

Below is a summary of the benefits of flu vaccination and selected scientific studies that support these benefits.

• Flu vaccination can keep you from getting sick with flu.
  • Flu vaccine prevents millions of illnesses and flu-related doctor’s visits each year. For example, during 2019-2020, the last flu season prior to the COVID-19 pandemic, flu vaccination prevented an estimated 7.5 million influenza illnesses, 3.7 million influenza-associated medical visits, 105,000 influenza-associated hospitalizations, and 6,300 influenza-associated deaths.
  • During seasons when flu vaccine viruses are similar to circulating flu viruses, flu vaccine has been shown to reduce the risk of having to go to the doctor with flu by 40% to 60%.
• Flu vaccination has been shown in several studies to reduce severity of illness in people who get vaccinated but still get sick.
  • A 2021 study showed that among adults hospitalized with flu, vaccinated patients had a 26% lower risk of intensive care unit (ICU) admission and a 31% lower risk of death from flu compared with those who were unvaccinated.
  • A 2018 study showed that among adults hospitalized with flu, vaccinated patients were 59% less likely to be admitted to the ICU than those who had not been vaccinated. Among adults in the ICU with flu, vaccinated patients on average spent four fewer days in the hospital than those who were not vaccinated.
• Flu vaccination can reduce the risk of flu-associated hospitalization.
  • Flu vaccine prevents tens of thousands of hospitalizations each year. For example, during 2019-2020 flu vaccination prevented an estimated 105,000 flu-related hospitalizations.
  • A 2018 study showed that from 2012 to 2015, flu vaccination among adults reduced the risk of being admitted to an ICU with flu by 82%.
  • A 2017 study found that during 2009-2016, flu vaccines reduced the risk of flu-associated hospitalization among older adults by about 40% on average.
  • A 2014 study showed that flu vaccination reduced children’s risk of flu-related pediatric intensive care unit (PICU) admission by 74% during flu seasons from 2010-2012.
• Flu vaccination is an important preventive tool for people with certain chronic health conditions.
  • Flu vaccination has been associated with lower rates of some cardiac events among people with heart disease, especially among those who have had a cardiac event in the past year.
  • Flu vaccination can reduce the risk of a flu-related worsening of chronic lung disease (for example, chronic obstructive pulmonary disease (COPD) requiring hospitalization).
  • Among people with diabetes and chronic lung disease, flu vaccination has been shown in separate studies to be associated with reduced hospitalizations from a worsening of their chronic condition.
• Flu vaccination during pregnancy helps protect pregnant people from flu during and after pregnancy and helps protect their infants from flu in their first few months of life.
  • Vaccination reduces the risk of flu-associated acute respiratory infection in pregnant people by about one-half.
  • A 2018 study showed that getting a flu shot reduced a pregnant person’s risk of being hospitalized with flu by an average of 40% from 2010-2016.
  • A number of studies have shown that in addition to helping to protect pregnant people from flu, a flu vaccine given during pregnancy helps protect the baby from flu for several months after birth, when babies are too young to be vaccinated.
• Flu vaccine can be lifesaving in children.
  • A 2022 study showed that flu vaccination reduced children’s risk of severe life-threatening influenza by 75%.
  • A 2020 study found that during the 2018-2019 flu season, flu vaccination reduced flu-related hospitalization by 41% and flu-related emergency department visits by half among children (aged 6 months to 17 years old).
  • A 2017 study was the first of its kind to show that flu vaccination can significantly reduce children’s risk of dying from flu.
• Getting vaccinated yourself may also protect people around you, including those who are more vulnerable to serious flu illness, like babies and young children, older people, and people with certain chronic health conditions.

Despite the many benefits offered by flu vaccination, only about half of Americans get an annual flu vaccine. During an average flu season, flu can cause millions of illnesses, hundreds of thousands of hospitalizations and tens of thousands of deaths. Many more people could be protected from flu if more people got vaccinated.

*References for the studies listed above can be found at Publications on Influenza Vaccine Benefits.

Are flu vaccines effective against all types of flu and cold viruses?

Seasonal flu vaccines are designed to protect against infection and illness caused by the four flu viruses that research indicates will be most common during the upcoming flu season. Flu vaccines do not protect against infection and illness caused by other viruses that also can cause flu-like symptoms. There are many other viruses besides flu viruses that can result in flu-like illness* (also known as influenza-like illness or “ILI”) that spread during the flu season. These non-flu viruses include rhinovirus (one cause of the “common cold”) and respiratory syncytial virus (RSV), which is the most common cause of severe respiratory illness in young children, and a major cause of severe respiratory illness in adults 65 years and older.

Does flu vaccine effectiveness vary by type or subtype?

Yes. The amount of protection provided by a flu vaccine may vary by flu virus type or subtype or by vaccine, even when viruses used to make flu vaccines are similar (or ‘well matched’) to the influenza viruses that are causing illness that season. Since 2009, VE studies looking at how well flu vaccines protect against medically attended illness have suggested better protection against influenza B or influenza A(H1N1) viruses than against influenza A(H3N2) viruses. A study [505 KB, 10 pages] that looked at a number of VE estimates from 2004-2015 found average VE of 33% (CI = 26%–39%) against illnesses caused by H3N2 viruses, compared with 61% (CI = 57%–65%) against H1N1 and 54% (CI = 46%–61%) against influenza B virus illnesses. VE estimates were lower when viruses used to make vaccines were different (not well-matched) from the flu viruses causing illness that season, especially against A(H3N2) viruses. The same study found average VE of 23% (95% CI: 2% to 40%) against A(H3N2) viruses when circulating influenza viruses were not well-matched to the A(H3N2) viruses used to make that season’s flu vaccines.

Why is flu vaccine typically less effective against influenza A(H3N2) viruses?

There are a number of reasons why flu vaccine effectiveness against influenza A(H3N2) viruses may be lower.

1. While all flu viruses undergo frequent genetic changes, the changes that have occurred in influenza A(H3N2) viruses have more frequently resulted in differences between the virus components of the flu vaccine and circulating influenza viruses (i.e., antigenic change) compared with influenza A(H1N1) and influenza B viruses. That means that between the time when flu viruses are selected to begin producing vaccines and when flu vaccines are delivered, A(H3N2) viruses are more likely than A(H1N1) or influenza B viruses to have changed in ways that could impact how well the flu vaccines work.
2. Growth in eggs is part of the production process for most seasonal flu vaccines. While all influenza viruses undergo changes when they are grown in eggs, changes in influenza A(H3N2) viruses tend to be more likely to result in antigenic changes compared with changes in other influenza viruses. These so-called “egg-adapted changes” are present in vaccine viruses recommended for use in vaccine production and may reduce their potential effectiveness against circulating influenza viruses. Other vaccine production technologies, e.g., cell-based vaccine production or recombinant flu vaccines, do not use eggs in vaccine production to avoid egg-adapted changes to the viruses used to make vaccines. CDC also is using advanced molecular techniques to improve flu vaccines.

How effective are flu vaccines in older adults?

In numerous studies since 2010, flu vaccines have helped protect older adults against influenza. Flu vaccination has reduced the risk of medically attended illness caused by A(H1N1) or influenza B viruses by more than 60% among people 65 years and older (1). Flu vaccines also have reduced the risk of flu hospitalization among adults 65 years and older due to A(H1N1) and influenza B(2). However, protection against influenza A(H3N2) viruses has been less consistent. On average, flu vaccines have reduced the risk of doctor visits for people with A(H3N2) flu by 24% and reduced the risk of hospitalization with A(H3N2) flu by 33% in adults 65 years and older (1,2). During seasons when the H3N2 vaccine component has been well-matched to the flu viruses circulating in the community, the benefit from flu vaccination has been higher. During these seasons, flu vaccine reduced the risk of hospitalization with A(H3N2) flu by 43% on average (2). But when the vaccine component was less similar to viruses in the community, the protection has dropped to 14% (2).For older adults, some studies have shown that some newer vaccines (the high-dose inactivated vaccine, the adjuvanted inactivated vaccine, and the recombinant influenza vaccine) might be more effective than standard-dose inactivated vaccines without an adjuvant. Because flu viruses and effectiveness of flu vaccines can vary from one season to another, it isn’t known whether any one of these vaccines will always be more effective in every flu season.

For the 2022-2023 flu season, CDC and the Advisory Committee on Immunization Practices (ACIP) have made a preferential recommendation for higher dose and adjuvanted flu vaccines for people aged 65 years and older. The preference applies to Fluzone High-Dose Quadrivalent vaccine, Flublok Quadrivalent recombinant flu vaccine and Fluad Quadrivalent adjuvanted flu vaccines. This recommendation was based on a review of available studies which suggests that, in this age group, these vaccines are potentially more effective than standard dose unadjuvanted flu vaccines. If one of the three preferentially recommended flu vaccines for people 65 and older is not available at the time of administration, people in this age group should get an age-appropriate standard-dose flu vaccine instead.

If older people have weaker immune responses to flu vaccination, should they still get vaccinated?

Despite the fact that some older adults (people 65 years and older) have weaker immune responses to the influenza A(H3N2) component of flu vaccines, there are many reasons why people in this age group should be vaccinated each year.

• First, people 65 years and older are at increased risk of serious illness, hospitalization and death from flu.
• Second, while the effectiveness of flu vaccines can be lower among some older people (particularly against influenza A(H3N2) viruses), there are seasons when significant benefit can be observed (this is particularly true against influenza A(H1N1) and influenza B viruses).
• Third, flu vaccination has been shown in several studies to reduce severity of illness in people who get vaccinated but still get sick.
• Flu vaccines can protect against more serious outcomes like hospitalization and death. For example, one study concluded that one death was prevented for every 4,000 people vaccinated against flu (1).
• Fourth, in adults 65 years and older, hospitalizations can mark the beginning of a significant decline in overall health and mobility, potentially resulting in loss of the ability to live independently or to complete basic activities of daily living. While the protection older adults obtain from flu vaccination can vary significantly, a yearly flu vaccination is still the best protection currently available against flu.
• In addition, it’s important to remember that people who are 65 and older are a diverse group and often are different from one another in terms of their overall health, level of activity and mobility, and behavior when it comes to seeking medical care. This group includes people who are healthy and active and have responsive immune systems, as well as those who have underlying medical conditions that may weaken their immune system and their bodies’ ability to respond to vaccination. Therefore, when evaluating the benefits of flu vaccination, it is important to look at a broader picture than what one study’s findings can present.

How effective are flu vaccines in children?

Vaccination has been found during most seasons to provide a similar level of protection against flu illness in children to that seen among adults.

In several studies, flu vaccine effectiveness was higher among children who received two doses of flu vaccine the first season that they were vaccinated (as recommended) compared to “partially vaccinated” children who only received a single dose of flu vaccine. However, in some seasons, partially vaccinated children still receive some protection.

In addition to preventing illness, flu vaccine can prevent severe, life-threatening complications in children, for example:

• A 2014 study showed that flu vaccine reduced children’s risk of flu-related pediatric intensive care unit (PICU) admission by 74% during flu seasons from 2010-2012.
• In 2017, a study in the journal Pediatrics was the first of its kind to show that flu vaccination also significantly reduced a child’s risk of dying from flu. The study, which looked at data from four flu seasons between 2010 and 2014, found that flu vaccination reduced the risk of flu-associated death by half (51 percent) among children with underlying, higher risk medical conditions and by nearly two-thirds (65 percent) among healthy children.

How are benefits of vaccination measured?

Public health researchers measure how well flu vaccines work through different kinds of studies. In “randomized studies,” flu vaccination is randomly assigned, and the number of people who get flu in the vaccinated group is compared to the number who get flu in the unvaccinated or placebo group. Randomized studies are the “gold standard” (best method) for determining how well a vaccine works. The effects of vaccination measured in these studies is called “vaccine efficacy.” Randomized, placebo-controlled studies are expensive and are not conducted after a recommendation for vaccination has been issued, as withholding vaccine from people recommended for vaccination would place them at risk for infection, illness and possibly serious complications. For that reason, most U.S. studies of vaccine benefits conducted after a vaccine is licensed and recommended are “observational studies.” Observational studies look at a group of people in a real world setting and compare the occurrence of flu illness in vaccinated people to unvaccinated people. This means that vaccination of study subjects is not randomized. The measurement of vaccine effects in an observational study is referred to as “vaccine effectiveness.”

How does CDC measure how well flu vaccines work?

CDC typically presents vaccine effectiveness (VE) as a single point estimate: for example, 60%. This point estimate represents the reduction in risk provided by a flu vaccine. CDC vaccine effectiveness studies measure different outcomes. For example, outcomes measured can include laboratory-confirmed flu illness (that results in a doctor’s visit), hospitalizations or intensive care unit (ICU) admissions. For these outcomes, a VE point estimate of 60% means that on average the flu vaccine reduces a person’s risk of that flu outcome by 60%.

In addition to the VE point estimate, CDC also provides a “confidence interval” (CI) for this point estimate, for example, 60% (95% CI: 50%-70%). The confidence interval provides a lower boundary for the VE estimate (e.g., 50%) as well as an upper boundary (e.g., 70%). One way to interpret a 95% confidence interval is that if CDC were to repeat this study 100 times , 95 times out of 100, the confidence interval would contain the true VE value. Another way to look at this is that there is a 95% chance that the true VE lies within the range described by the confidence interval. This means there is still the possibility that five times out of 100 (a 5% chance) the true VE value could fall outside of the 95% confidence interval.

Why are confidence intervals important for understanding flu vaccine effectiveness?

Confidence intervals are important because they provide context for understanding the precision or exactness of a VE point estimate. The wider the confidence interval, the less exact the point value estimate of vaccine effectiveness becomes. Take, for example, a VE point estimate of 60%. If the confidence interval of this point estimate is 50%-70%, then we can have greater certainty that the true protective effect of the flu vaccine is near 60% than if the confidence interval were between 10% and 90%. Furthermore, if a confidence interval crosses zero, for example, (-20% to 60%), then the point value estimate of VE provided is considered “not statistically significant.” People should be cautious when interpreting VE estimates that are not statistically significant because such results cannot rule out the possibility of zero VE (i.e., no protective benefit). The width of a confidence interval is related in part to the number of participants in the study, and so studies that provide more precise estimates of VE (and consequently, have a narrower confidence interval) typically include a larger number of participants.

Is it true that getting vaccinated repeatedly can reduce vaccine effectiveness?

A report examining studies from the 2010-2011 to the 2014-2015 seasons concluded that the effectiveness of a flu vaccine may be influenced by vaccination the prior season or during many prior seasons (1,2). In some seasons, protection against influenza A(H3N2) virus illness may have been lower for people vaccinated in the current season and the prior season compared with those who had only been vaccinated in the current season. This fits with findings on immune response to vaccination that suggest repeated influenza vaccination can weaken the immune response to vaccination and especially to the H3N2 vaccine component. However, repeated annual vaccination also can be beneficial during some seasons, since sometimes people retain and carry over immune protection from one season to the next. During some seasons, people who missed getting vaccinated still had residual protection against influenza illness.

Information regarding flu vaccination history is particularly important to these types of evaluations, and can be difficult to confirm, as accurate vaccination records are not always readily available. People who choose to get vaccinated every year may have different characteristics and susceptibility to flu compared to those who do not seek vaccination every year. CDC supports continued efforts to monitor the effects of repeat vaccination each year in part to understand the immune response to repeat vaccination better. However, based on the substantial burden of flu in the United States, and on the fact that most studies point to vaccination benefits, CDC recommends that yearly flu vaccination is the first and most important action people can take to protect against flu and its potentially serious complications.

Why are there so many different outcomes for vaccine effectiveness studies?

Vaccine effectiveness studies that measure different outcomes are conducted to better understand the different kinds of benefits provided by vaccination. Ideally, public health researchers want to evaluate the benefits of vaccination against illness of varying severity. To do this, they assess how well flu vaccines work to prevent illness resulting in a doctor visit, or illness resulting in hospitalization, ICU admission, and even death associated with flu. Because estimates of vaccine effectiveness may vary based on the outcome measured (in addition to season, population studied, and other factors), results should be compared between studies that used the same outcome for estimating vaccine effectiveness.

How does CDC measure how well the vaccine works?

Scientists continue to work on better ways to design, conduct and evaluate non-randomized (i.e., observational) studies to assess how well flu vaccines work. CDC has been working with researchers at universities and hospitals since the 2003-2004 flu season to estimate how well flu vaccine works through observational studies using laboratory-confirmed flu as the outcome. These studies currently use a very accurate and sensitive laboratory test known as real-time RT-PCR (reverse transcription polymerase chain reaction) to confirm medically attended flu virus infections as a specific outcome. CDC’s studies are conducted in sites located across the United States to gather data that accurately represents people and conditions across the country. To assess how well the vaccine works across different age groups, CDC’s studies of flu vaccine effects have included all people aged 6 months and older recommended for an annual flu vaccination. Similar studies are being done in Australia, Canada and Europe.

Over the past few years, CDC has conducted VE studies using multiple networks, including the U.S. Flu VE Network, the Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN), the Influenza and Other Viruses in the Acutely Ill (IVY) network, the National Vaccine Surveillance Network (NVSN), and the VISION VE Network. For this upcoming winter, HAIVEN will no longer be used. HAIVEN looked at how well flu vaccines protect against flu-related hospitalization among adults aged 18 and older. HAIVEN ended enrollment on July 31, 2021, but CDC will continue to collect information on adults hospitalized with flu through its other VE networks, including IVY and VISION. IVY consists of 21 large, adult hospitals in 20 U.S. cities and was originally created in 2019 to estimate how well the flu vaccine works at preventing severe flu illness among intensive care unit (ICU) patients. As of April 1, 2021, IVY has expanded to enroll all adults hospitalized with COVID-19. During the 2021-2022 flu season, the network will also enroll patients hospitalized with flu. NVSN collects vaccine effectiveness data on pediatric hospitalizations with laboratory confirmed flu in children 18 years of age and younger. The VISION VE Network collects data on emergency department visits, hospitalizations, and intensive care unit (ICU) admissions.

What do recent vaccine effectiveness studies show?

Recent studies show flu vaccine can reduce the risk of flu illness by between 40% and 60% among the overall population during seasons when most circulating flu viruses are well matched to the flu vaccine viruses.

Do recent vaccine effectiveness study results support flu vaccination?

The large numbers of flu-associated illnesses and deaths in the United States, combined with the evidence from many studies that show flu vaccines help to protect against flu illness and its potentially serious complications, support the current U.S. flu vaccination recommendations. CDC recommends a yearly flu vaccine as the first and most important step in protecting against flu viruses. Everyone 6 months and older should get an annual flu vaccine, ideally by the end of October.

Besides vaccination, how can people protect themselves against the flu?

Getting a flu vaccine each year is the best way to prevent the flu. In addition to getting the flu shot, people should take the same everyday preventive actions to prevent the spread of flu, including covering coughs, washing hands often, and avoiding people who are sick. Antiviral drugs are an important second line of defense to treat the flu. These drugs are not a substitute for vaccination and must be prescribed by a health care provider.

Are flu vaccines safe?

Flu vaccines have a good safety record. Hundreds of millions of Americans have safely received flu vaccines over the past 50 years, and there has been extensive research supporting the safety of flu vaccines.

A flu vaccine is the first and best way to reduce your chances of getting the flu and spreading it to others. CDC recommends that everyone 6 months of age and older receive a flu vaccine every year.

Can I get the flu from the flu vaccine?

No, the flu vaccine cannot cause flu. The vaccines either contain inactivated virus, meaning the viruses are no longer infectious, or a particle designed to look like a flu virus to your immune system. While the nasal spray flu vaccine does contain a live virus, the viruses are changed so that they cannot give you the flu.

Do flu vaccines cause any side effects?

Like any medical product, vaccines can cause side effects. Side effects of the flu vaccine are generally mild and go away on their own within a few days.

Common side effects from the flu shot include:

• Soreness, redness, and/or swelling from the shot
• Headache
• Fever
• Nausea
• Muscle aches

The flu shot, like other injections, can occasionally cause fainting.

Some studies have found a possible small association of injectable flu vaccine with Guillain-Barré syndrome (GBS). Overall, these studies estimated the risk for GBS after vaccination as fewer than 1 or 2 cases of GBS per one million people vaccinated. Other studies have not found any association. GBS also, rarely, occurs after flu illness. Even though GBS following flu illness is rare, GBS is more common following flu illness than following flu vaccination. GBS has not been associated with the nasal spray vaccine.

Are there signs or symptoms that should cause concern after getting a flu vaccine?

With any vaccine, look for any unusual conditions, such as a high fever, behavior changes, or signs of a severe allergic reaction after vaccination.

Signs of a severe allergic reaction can include:

• Difficulty breathing
• Hoarseness or wheezing
• Swelling around the eyes or lips
• Hives
• Paleness
• Weakness
• A fast heart beat or dizziness

Life threatening allergic reactions to the flu shot are rare. These signs would most likely happen within a few minutes to a few hours after the vaccine is given.

What should I do if I think I am having a severe reaction to a flu vaccine?

If you think it is a severe allergic reaction or other emergency that can’t wait, call 9-1-1 and get to the nearest hospital. Otherwise, call your doctor.

Afterward, the reaction should be reported to the Vaccine Adverse Event Reporting System (VAERS). Your doctor might file this report, or you can do it yourself through the VAERS website, or by calling 1-800-822-7967.

What should I do if I think I have been injured by the flu vaccine?

If you believe you have been injured by a flu vaccine you may be eligible to receive compensation from the federal government for your injuries if certain criteria are met. To learn more visit the National Vaccine Injury Compensation Program website or call 1-800-338-2382.

Are there some people who should not receive a flu vaccine?

CDC recommends everyone 6 months of age and older should receive an annual flu vaccination with rare exceptions. Individuals who can’t get the flu shot include:

• Children younger than 6 months, since they are too young to get a flu shot.
• Individuals with severe, life-threatening allergies to flu vaccine or any ingredient(s) in the vaccine.

Individuals should talk with their doctor before getting the flu shot if they:

• Have had a severe allergy to eggs or any of the ingredients in the vaccine.
  • See Special Considerations Regarding Egg Allergy for more information about egg allergies and flu vaccine.
• Have had Guillain-Barré syndrome (GBS).
• Are not feeling well.

There are multiple flu vaccines available, and not all flu vaccines can be given to people of all ages. Talk to your doctor if you have any questions regarding which flu vaccine options are best for you and your family. See Vaccination: Who Should Do It, Who Should Not and Who Should Take Precautions) for more information.

Should pregnant women receive a flu vaccine?

Yes, pregnant women should get a flu shot to protect themselves and their developing babies. To learn more about flu vaccine safety during pregnancy, visit Flu Vaccine Safety and Pregnancy.

How is the safety of flu vaccines monitored?

CDC and the Food and Drug Administration (FDA) closely monitor the safety of vaccines approved for use in the United States. CDC uses two primary systems to monitor the safety of flu vaccines:

1. Vaccine Adverse Event Reporting System (VAERS): an early warning system that helps CDC and FDA monitor problems following vaccination. Anyone can report possible vaccine side effects to VAERS. Generally, VAERS reports cannot determine if an adverse event was caused by a vaccine, but these reports can help determine if further investigations are needed.
2. Vaccine Safety Datalink (VSD): A collaboration between CDC and nine health care organizations which allows ongoing monitoring and proactive searches of vaccine-related data.

People with egg allergies can receive any licensed, recommended age-appropriate influenza (flu) vaccine (IIV4, RIV4, ccIIV4, or LAIV4) that is otherwise appropriate. People who have a history of severe egg allergy (those who have had any symptom other than hives after exposure to egg) should be vaccinated in a medical setting, supervised by a health care provider who is able to recognize and manage severe allergic reactions. Two completely egg-free flu vaccine options are available: Flublok Quadrivalent recombinant flu vaccine and Flucelvax Quadrivalent cell-based flu shot.

A yearly flu vaccine is the best way to protect your child from flu and its potentially serious complications.

Why should my child get a flu vaccine?

• Reduces the risk of flu illness and hospitalization among children.
• Shown to be life-saving for children.
• Can make illness less severe among people who get vaccinated but still get sick with flu.
• Reduces the risk of illness, which can keep your child from missing school or childcare and you from having to miss work.
• Reduces the high risk of developing serious flu complication especially if your child is younger than 5 years, or of any age with certain chronic conditions.
• Helps prevent spreading flu to family and friends, including babies younger than 6 months who are too young to get a flu vaccine.

When should my child get a flu vaccine?

Doctors recommend that your child get a flu vaccine every year in the fall, starting when he or she is 6 months old. Some children 6 months through 8 years of age may need 2 doses for best protection.

• CDC recommends a flu vaccine by the end of October, before flu begins spreading in your community. Getting vaccinated later, however, can still be beneficial and vaccination should continue to be offered throughout the flu season, even into January or later.
• Children 6 months through 8 years getting a flu vaccine for the first time, and those who have only previously gotten one dose of flu vaccine, should get two doses of vaccine. The first dose should be given as soon as vaccine becomes available.
• If your child previously got two doses of flu vaccine (at any time), he only needs one dose of flu vaccine this season.

CDC recommends a yearly flu vaccine for everyone ages six months and older. Pregnant women should get a flu vaccine during each pregnancy. Flu vaccines given during pregnancy help protect both the mother and her baby from flu.

What vaccines protect against flu?

For the 2020-2021 flu season, CDC recommends a yearly flu vaccination for everyone 6 months and older.

• Flu shots can be given to your child 6 months and older.
• The nasal spray vaccine can be given to people 2 through 49 years of age. However, certain people with underlying medical conditions should not get the nasal spray vaccine.

Your child’s doctor will know which vaccines are right for your child.

Should I get vaccinated if I’m pregnant?

Yes. Changes in your immune, heart, and lung functions during pregnancy make you more likely to get seriously ill from flu. CDC recommends pregnant women get a yearly seasonal flu shot by the end of October, if possible, to ensure best protection against flu. You can be vaccinated during any trimester of your pregnancy. Getting vaccinated can also help protect your baby after birth from flu. (Mom passes antibodies onto the developing baby during her pregnancy.)

Flu vaccines are very safe.

Flu vaccines have a good safety record. Hundreds of millions of Americans have safely received flu vaccines for more than 50 years, and there has been extensive research supporting the safety of flu vaccines.

Vaccines, like any medicine, can have side effects. When they occur, flu vaccine side effects are generally mild and go away on their own within a few days.

What are the side effects?

Common side effects from the flu shot may include:

• Soreness, redness, and/or swelling where shot was given
• Headache
• Fever
• Nausea
• Muscle aches

Side effects from the nasal spray flu vaccine may include:

• Runny nose
• Wheezing
• Headache
• Vomiting
• Muscle aches

If these problems occur, they usually begin soon after vaccination and are mild and short-lived.

To prevent fainting and injuries related to fainting, adolescents should be seated or lying down during vaccination and remain in that position for 15 minutes after the vaccine is given.

Why does my child need a flu vaccine every year?

Flu viruses are constantly changing, so new vaccines are made each year to protect against the flu viruses that are likely to cause the most illness. Also, protection provided by flu vaccination wears off over time. Your child’s flu vaccine will protect against flu all season, but they will need a vaccine again next flu season for best protection against flu.

What is flu?

Flu—short for influenza—is an illness caused by influenza viruses. Flu viruses infect the nose, upper airways, throat, and lungs. Flu spreads easily and can cause serious illness, especially for young children, older people, pregnant women, and people with certain chronic conditions like asthma and diabetes.

What are the symptoms of flu?

Flu symptoms can include:

• Fever (not everyone with flu will have a fever) or feeling feverish/chills
• Chills
• Cough
• Sore throat
• Runny or stuffy nose
• Headache
• Muscle or body aches
• Tiredness
• Vomiting and/or diarrhea (this is more common in children than adults)

Most people who get sick with flu will recover in a few days to less than two weeks.

Is flu illness serious?

Millions of children get sick with flu each year and thousands are hospitalized. CDC estimates that since 2010, between 7,000 and 28,000 children younger than 5 years old have been hospitalized for flu each year in the United States. Children with chronic conditions like asthma, diabetes, and disorders of the brain or nervous system, and children younger than 5 years old (and especially children younger than 2 years old) are more likely to end up in the hospital from flu.

Some people at high risk can develop complications (such as pneumonia) that can result in hospitalization and even death.

Flu seasons vary in how serious they are from one season to another. Since 2010, CDC estimates that between 130 and 1,200 children (younger than 18 years) have died from flu each year.

How does flu spread?

Flu spreads mainly by droplets when people who have flu talk, cough, or sneeze, and these droplets land in the mouths or noses of people who are nearby or are inhaled. Less often, a person might get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes.

People can spread flu to others from one day before they have symptoms to 5-7 days after they get sick. This can be longer in children and people who are very sick.

Can my child get flu from a flu vaccine?

No, flu vaccines do not cause flu. Flu vaccines (given as a shot) are currently made in two ways: the vaccine is made either with

1. flu viruses that have been ‘inactivated’ (killed) and are therefore not infectious, or
2. using only a single gene from a flu virus (as opposed to the full virus) in order to produce an immune response without causing infection.

Flu vaccine protects your child from flu illness. However, flu shots can sometimes cause mild side effects that may be mistaken for flu. Keep in mind that it will take about 2 weeks after getting a vaccine for your child to build protection against flu.

The single best way to reduce the risk of seasonal flu and its potentially serious complications is to get vaccinated each year, but good health habits like avoiding people who are sick, covering your cough and washing your hands often can help stop the spread of germs and prevent respiratory illnesses like flu. There also are flu antiviral drugs that can be used to treat and prevent flu.

The tips and resources below will help you learn about actions you can take to protect yourself and others from flu and help stop the spread of germs.

1. 1. Avoid close contact.
      Avoid close contact with people who are sick. When you are sick, keep your distance from others to protect them from getting sick too.
   2. Stay home when you are sick.
      If possible, stay home from work, school, and errands when you are sick. This will help prevent spreading your illness to others.
   3. Cover your mouth and nose.
      Cover your mouth and nose with a tissue when coughing or sneezing. It may prevent those around you from getting sick. Flu viruses spread mainly by droplets made when people with flu cough, sneeze or talk.
   4. Clean your hands.
      Washing your hands often will help protect you from germs. If soap and water are not available, use an alcohol-based hand rub.
   5. Avoid touching your eyes, nose or mouth.
      Germs can be spread when a person touches something that is contaminated with germs and then touches his or her eyes, nose, or mouth.
   6. Practice other good health habits.
      Clean and disinfect frequently touched surfaces at home, work or school, especially when someone is ill. Get plenty of sleep, be physically active, manage your stress, drink plenty of fluids, and eat nutritious food.

In the context of the COVID-19 pandemic, local governments or public health departments may recommend additional precautions be taken in your community. Follow those instructions.

Preventing Flu at Work and School

At School

• Find out about plans your child’s school, childcare program, and/or college has if an outbreak of flu or another illness occurs and whether flu vaccinations are offered on-site.
• Make sure your child’s school, childcare program, and/or college routinely cleans frequently touched objects and surfaces, and that they have a good supply of tissues, soap, paper towels, alcohol-based hand rubs, and disposable wipes on-site.
• Ask how sick students and staff are separated from others and who will care for them until they can go home, and about the absentee policy for sick students and staff.

At Work

• Find out about your employer’s plans if an outbreak of flu or another illness occurs and whether flu vaccinations are offered on-site.
• Routinely clean frequently touched objects and surfaces, including doorknobs, keyboards, and phones, to help remove germs.
• Make sure your workplace has an adequate supply of tissues, soap, paper towels, alcohol-based hand rubs, and disposable wipes.
• Train others on how to do your job so they can cover for you in case you or a family member gets sick and you have to stay home.
• If you begin to feel sick while at work, go home as soon as possible.

You can reduce the spread of flu this year. Protect yourself, your family, your neighborhood and community from the flu. “Step up” to prevent flu!

Step 1: Get your flu shot

Everyone age 6 months and older should get a flu shot every year. Getting a flu shot is the best way to slow the spread of flu. Learn more about flu vaccination.

Step 2: Know how flu is spread

When a person with flu sneezes, coughs, talks, or laughs, flu virus can spread into the air as droplets. The droplets can spread to people and surfaces up to 6 feet away. Flu virus can spread to your hands if you touch anything that has the virus on it. If you then touch your eyes, nose, or mouth, you might get the flu.

People can spread flu to others about 1 day before they feel sick and up to 5 days after getting sick.

Step 3: Know the symptoms of flu

Symptoms include a fever (100°F or higher), body and muscle aches, headache, feeling tired or weak, cough, sore throat, runny or stuffy nose, nausea and vomiting. Find out more about flu, including the differences between colds and flu.

Step 4: Clean your hands and surfaces around you

Clean hands often by washing with soap and water or by using hand sanitizers. Clean hands before eating or preparing food, before and after caring for someone who is sick, after coughing or sneezing, and after using the bathroom.

Clean surfaces that are touched often such as phones, faucets, light switches, countertops, door and cabinet handles, keyboard and mouse, and TV remotes. Flu virus can live on surfaces for up to 48 hours.

Step 5: Cover your coughs and sneezes

Use clean tissues and discard after each use. Cough or sneeze into your sleeve when you don't have a tissue.

Always clean your hands after coughing or sneezing.

Step 6: Stay home when sick

Because flu spreads easily from person to person, stay home when you are sick. Studies show you are most contagious and likely to spread flu virus to others for at least 5 days after your first symptoms start and at least 48 hours after your last fever.

Treat flu by getting plenty of rest, drinking fluids, and using medicines that reduce fevers. Find out more about treating flu and when to seek medical care.