Influenza, also known as the flu, is a contagious respiratory disease that is caused by influenza viruses. Influenza viruses infect the respiratory tract (nose, throat, and lungs) in humans. The flu is different from a cold, mainly because the symptoms and complications are more severe. Influenza usually comes on suddenly and may include these symptoms: fever, headache, malaise (a feeling of being ill and without energy that can be extreme), cough, sore throat, nasal congestion and body aches.

A lot of the illness and death caused by the influenza virus can be prevented by a yearly influenza vaccine. Most individuals 6 months of age and older should get the influenza vaccine every year. It is especially important for people in high-risk groups and people who are in close contact with those at high risk to get an influenza vaccine every year as recommended by CDC’s Advisory Committee on Immunization Practices (ACIP).

Influenza vaccine can be given to most individuals 6 months of age and older to protect against influenza. Persons who provide important community services (such as police, fire department personnel, emergency medical services) should consider getting an influenza vaccine so that those services are not disrupted during an influenza outbreak.

Influenza (flu) is a common contagious viral respiratory illness that can affect the nose, throat, and lungs. Flu viruses spread mainly by droplets made when people with flu cough, sneeze or talk. Flu illness can vary from mild to severe. When severe, flu can result in hospitalization and even death. Some people are more likely to suffer serious flu complications, including older adults, pregnant people, young children and people with certain chronic health conditions. CDC recommends that everyone 6 months and older get an annual flu vaccine. Flu vaccination can prevent flu illness and its potentially serious complications. While flu vaccination varies in how well it works, an annual flu vaccination is the best way to protect against flu. However, if you get the flu, there are medications that can help treat it, and which are particularly important for some groups of people. Influenza antiviral drugs are prescription medications that can reduce severity and duration of flu illness, and also might prevent serious flu complications. CDC recommends influenza antiviral treatment for people who are very sick with flu and people with flu symptoms who are at higher risk of developing serious flu complications.

Key Facts

• The severity of flu seasons can differ substantially from season to season.
• You may be able to spread flu to someone else before you know you are sick, as well as while you are sick.
• Hundreds of thousands of people are hospitalized with flu each year.
• People with certain long-term health conditions, like asthma or diabetes, are at higher risk of serious flu complications.
• Take 3 steps to fight flu: get vaccinated, take everyday preventive actions, and take antiviral medicines if prescribed.

Are you at higher risk?

Certain people are at a greater risk of developing serious flu complications. These groups of people include: children younger than 5, adults 65 years of age or older, pregnant women, and people with certain chronic health conditions.

Prevention Tips

• An annual flu vaccination is the best way currently available to reduce the risk from flu and its potentially serious complications. As long as flu viruses are spreading, you can still benefit from a flu vaccine.
• Avoid people who are sick. Stay home when you are sick with flu for at least 24 hours after your fever is gone, except to get medical care or other necessities. Your fever should be gone without the need to use a fever-reducing medicine, such as acetaminophen.
• Avoid touching your eyes, nose, or mouth. Though less common than spread through droplets that come from the nose and mouth when people cough, sneeze, or talk, flu viruses can also when a person touches something that is contaminated with flu viruses and then touches their eyes, nose, or mouth.
• Wash your hands regularly with soap and water. If soap and water are not available, use an alcohol-based hand rub.
• Check with your doctor promptly if you are at higher risk of developing serious flu complications and you get flu symptoms. Your doctor may prescribe influenza antiviral drugs to treat your flu illness, which can lessen the severity of your illness, shorten the amount of time you are sick and help prevent serious flu complications.

The influenza, or flu, vaccine you get at your doctor’s office or pharmacy is the year-round work of highly skilled microbiologists, epidemiologists, physicians and other public health experts.

Sound complicated? It is.

The U.S. Food and Drug Administration and the U.S. Department of Health and Human Services (HHS) are working toward developing new and better technologies for producing flu vaccines. As new strains of flu viruses emerge, the FDA works in close coordination with sister agencies, such as the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH), encouraging manufacturers to develop vaccines that will successfully protect us from influenza disease, which can be a very serious illness.

The more diverse the influenza vaccine supply, the better we can respond to flu public health emergencies. All FDA-approved flu vaccines have been evaluated and determined to be safe and effective by the agency.

There is often more than one type of influenza virus circulating each season. So, vaccines are formulated to target four of the most likely influenza viruses to circulate and cause illness in the U.S. during the upcoming influenza season: two influenza A types (H1N1 and H3N2) and two types of influenza B. These are known as quadrivalent vaccines. Influenza B more commonly affects children and also causes more complications and death in children than adults.

Influenza Vaccines and How They Are Made

The influenza vaccine works by triggering your immune system to produce antibodies that help the body prevent the flu.

Most of the U.S. influenza vaccine supply is made using an egg-based production process. In this method, manufacturers use fertilized eggs to grow flu viruses. After about six months of laboratory work and manufacturing, those viruses are incorporated into that season’s flu vaccine.

Although this method produces safe and effective vaccines, the FDA, HHS and manufacturers have been working on different technologies to increase the influenza vaccine supply, making sure to still maintain safety and effectiveness. Some technologies have the potential to produce these vaccines faster and more efficiently. For example, the FDA has approved influenza vaccines that do not use an egg-based production process for manufacturing.

In addition, the FDA has approved a high-dose and an adjuvanted vaccine specifically for people ages 65 and older, who typically bear the greatest burden of severe influenza disease and account for most of flu-related hospitalizations and deaths. Adjuvants are incorporated into some vaccine formulations to enhance the immune response of the vaccinated person.

Making the Flu Vaccine: A Year-Round Effort

The job of producing a new vaccine for the next flu season starts well before the current flu season ends. For the FDA, it’s a year-round initiative.

Flu viruses are constantly evolving. And the flu viruses that circulate and cause disease in people often change from one year to another. We need a new flu vaccine every year.

To that end, the FDA, World Health Organization (WHO), CDC and other partners collaborate by collecting and reviewing data on the circulating strains of influenza from around the world to identify those likely to cause the most illness in the upcoming flu season.

In late February/early March — well before the new flu season begins — an FDA advisory committee reviews data about which flu viruses have caused disease in the past year, how the viruses are changing, and disease trends so they can recommend the flu virus strains to include in the influenza vaccines for the U.S. in the upcoming flu season.

Once the strains are selected, vaccine producers begin the manufacturing process to include the newly selected flu strains in their FDA-approved vaccines. The different flu virus strains are combined to formulate the vaccine into standard dosages. The vaccine is then filled into vials, syringes and, for the nasal vaccine, sprayers.

Both egg-based and non-egg-based manufacturing methods for FDA-approved flu vaccines require high-tech processes and manufacturing facilities that have been inspected by the FDA. Vaccine manufacturers must submit applications to the FDA that include the new flu strains in their FDA-approved vaccines and updated prescribing information.

In its own laboratories, the FDA also produces materials that are critical for making the vaccine. These include generating candidate vaccine virus strains suitable for further vaccine manufacture and producing the critical potency reagents, which are materials needed to test the vaccines for potency and identity (to ensure standardization) before the FDA approves the new formulation of the approved seasonal influenza vaccines for U.S. distribution.

The FDA is also responsible for ensuring that released lots of influenza vaccines meet appropriate standards. Each vaccine undergoes quality control tests, including testing for sterility. Manufacturers submit the results of their testing, along with sample vials from each lot to the FDA for “lot release.”

The FDA typically begins releasing lots of flu vaccines in late summer. Lot release can continue into early fall. Once lots are released, manufacturers distribute the vaccine throughout the U.S. for use by the public.

A Flu Vaccine Is the Best Prevention

Flu seasons and severity are unpredictable. Annual vaccination is the best way to prevent the flu for people ages 6 months and older.

An annual immunization with flu vaccine is the most effective and safest way for most of us to reduce our risk of getting the flu and spreading it to others. When more people get vaccinated, it is less likely that the flu viruses will spread through a community, making us all healthier.

Updates to the Advisory Committee on Immunization Practices (ACIP) Flu Vaccine Recommendations for the 2023-2024 season

A couple of things are different for the 2023-2024 influenza (flu) season:

• The composition of flu vaccines has been updated. Flu vaccines for the U.S. 2023-2024 season will contain the following:
  Egg-based vaccines

• • • an A/Victoria/4897/2022 (H1N1)pdm09-like virus; (Updated)
    • an A/Darwin/9/2021 (H3N2)-like virus;
    • a B/Austria/1359417/2021 (B/Victoria lineage)-like virus; and
    • a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.
• Cell- or recombinant-based vaccines
  • • an A/Wisconsin/67/2022 (H1N1)pdm09-like virus; (Updated)
    • an A/Darwin/6/2021 (H3N2)-like virus;
    • a B/Austria/1359417/2021 (B/Victoria lineage)-like virus; and
    • a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.
    • These recommendations include one update compared to the 2022-2023 U.S. flu vaccine composition. The influenza A(H1N1)pdm09 vaccine virus component was updated for egg-based and cell- or recombinant-based flu vaccines.
• People with egg allergy may get any vaccine (egg-based or non-egg-based) that is otherwise appropriate for their age and health status. Previously, it was recommended that people with severe allergy to egg (those who have had any symptom other than hives with egg exposure) be vaccinated in an inpatient or outpatient medical setting. Beginning with the 2023-2024 season, additional safety measures are no longer recommended for flu vaccination of people with an egg allergy beyond those recommended for receipt of any vaccine, regardless of the severity of previous reaction to egg. All vaccines should be given in settings where allergic reactions can be recognized and treated quickly.

Projected U.S. Flu Vaccine Supply for the 2023-2024 Season

• Vaccine manufacturers have projected that they will supply the United States with as many as 156.2 million to 170 million doses of influenza vaccines for the 2023-2024 season. These projections may change as the season progresses.
  • All flu vaccines for the 2023-2024 season will be quadrivalent (four-component).
  • Most will be thimerosal-free or thimerosal-reduced vaccines (91%), and about 21% of flu vaccines will be egg-free.

What is a flu vaccine?

Influenza (flu) vaccines (often called “flu shots”) are vaccines that protect against the four influenza viruses that research indicates will be most common during the upcoming season. Most flu vaccines are “flu shots” given with a needle, usually in the arm, but there also is a nasal spray flu vaccine.

Is there more than one type of flu shot available?

Yes. There are different flu vaccine manufacturers and multiple flu vaccines that are licensed and recommended for use in the United States.

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.

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.

There are many flu vaccine options to choose from, but 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 vaccine is best for you, talk to your doctor or other health care professional.

Who should and who should not get a flu vaccine?

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.

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.

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 or Fluad Quadrivalent adjuvanted flu vaccine. On June 22, 2022, CDC’s Advisory Committee on Immunization Practices (ACIP) voted unanimously to preferentially recommend these vaccines over standard-dose unadjuvanted 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. There is no preferential recommendation for people younger than 65 years.

What if a preferentially recommended flu vaccine is not available?

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.

How effective is the seasonal flu shot?

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.

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.

What are the side effects that could occur?

Common side effects from a flu shot include soreness, redness, and/or swelling where the shot was given, headache (low grade), fever, nausea, muscle aches, and fatigue. The flu shot, like other injections, can occasionally cause fainting.

Can severe problems occur?

Life-threatening allergic reactions to flu shots are very rare. Signs of serious allergic reaction can include breathing problems, hoarseness or wheezing, hives, paleness, weakness, a fast heartbeat, or dizziness. If they do occur, it is usually within a few minutes to a few hours after receiving the shot. These reactions can occur among persons who are allergic to something that is in the vaccine, such as egg protein or other ingredients. While severe reactions are uncommon, you should let your doctor, nurse, clinic, or pharmacist know if you have a history of allergy or severe reaction to influenza vaccine or any part of flu vaccine.

There is a small possibility that flu vaccine could be associated with Guillain-Barré syndrome, generally no more than 1 or 2 cases per million people vaccinated. This is much lower than the risk of severe complications from flu, which can be prevented by flu vaccine.

What should I do if I have had a serious reaction to seasonal flu vaccine?

Call a doctor or get to a doctor right away.

Tell your doctor what happened, the date and time it happened, and when you got the flu shot.

Ask your doctor, nurse, or health department to file a Vaccine Adverse Event Reporting System (VAERS) form, or call VAERS at 1-800-822-7967. Reports are welcome from all concerned individuals: patients, parents, health care providers, pharmacists and vaccine manufacturers.

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

Flu vaccine side effects are generally mild and go away on their own within a few days. Some side effects that may occur from a flu shot include soreness, redness, and/or swelling where the shot was given, headache (low grade), fever, nausea, muscle aches, and fatigue. The flu shot, like other injections, can occasionally cause fainting.

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.

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

Some people who get vaccinated may still get sick. However, flu vaccination has been shown in several studies to reduce severity of illness in people who get vaccinated but still get sick:

• 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 flu patients.
• Another study in 2018 showed that a vaccinated adult who was hospitalized with flu was 59% less likely to be admitted to an intensive care unit (ICU) than someone who had not been vaccinated. Among adults in the ICU with flu, vaccinated patients on average spent 4 fewer days in the hospital than those who were not vaccinated.

In addition, it’s important to remember that flu vaccine protects against three or four different viruses and multiple viruses usually circulate during any one season. 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.

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.

Brand name: FluMist Quadrivalent

What flu viruses does the nasal spray vaccine protect against?

All nasal spray influenza (flu) vaccines for the 2022-2023 season are quadrivalent, meaning they are designed to protect against four flu viruses: an influenza A(H1N1) virus, an influenza A(H3N2) virus and two influenza B viruses.

Who can be vaccinated with the nasal spray flu vaccine?

The nasal spray flu vaccine is approved for use in healthy non-pregnant people, 2 through 49 years old. People with certain medical conditions should not get the nasal spray flu vaccine.

Who should not get the nasal spray flu vaccine?

Some people should not get the nasal spray flu vaccine:

• Children younger than 2 years old
• Adults 50 years and older
• People with a history of severe allergic reaction to any ingredient of the vaccine or to a previous dose of any flu vaccine
• Children 2 through 17 years old who are receiving aspirin- or salicylate-containing medications.
• Children 2 through 4 years old who have asthma or who have had a history of wheezing in the past 12 months
• People with weakened immune systems (immunosuppression) from any cause
• People who care for severely immunocompromised persons who require a protected environment (or otherwise avoid contact with those persons for 7 days after getting the nasal spray vaccine)
• People without a spleen, or with a non-functioning spleen
• Pregnant people
• People with an active leak between the cerebrospinal fluid and the mouth, nose, ear, or other place within the skull
• People with cochlear implants
• People who have taken flu antiviral drugs within a certain amount of time. (48 hours for oseltamivir and zanamivir, 5 days for peramivir, and 17 days for baloxavir.)

In addition, the following medical conditions are precautions to the use of the nasal spray flu vaccine:

• Asthma in people 5 years and older.
• Other underlying medical conditions that can put people at higher risk of serious flu complications. These include conditions such as lung disease, heart disease (except isolated hypertension), kidney disease (like diabetes), kidney or liver disorders, neurologic/neuromuscular, or metabolic disorders.
• Moderate or severe acute illness with or without fever.
• Guillain-Barré Syndrome within 6 weeks following a previous dose of flu vaccine.

How effective is the nasal spray seasonal flu vaccine?

Flu vaccine effectiveness (VE) can vary from year to year, among different age and risk groups, by vaccine type, and even by virus type and subtype. Prior to the 2009 flu pandemic, the nasal spray vaccine was found to be effective against different flu viruses. After the 2009 pandemic, several U.S. studies among 2 through 17-year-olds found that the nasal spray vaccine was as effective against influenza B viruses and influenza A(H3N2) viruses as inactivated influenza vaccines but was less effective than inactivated flu vaccines against the 2009 pandemic H1N1 viruses. These data led ACIP and CDC to recommend against use of the nasal spray vaccine for the 2016-17 and 2017-18 seasons.

Since the 2017-2018 season, the manufacturer of nasal spray vaccine has used new influenza A(H1N1) vaccine virus ingredients in production.  Because of limited use, there have been no effectiveness estimates in the United States since LAIV was recommended again in the 2018-2019 influenza season. Data from other countries have demonstrated protection from LAIV to be similar to that of standard-dose, egg-based inactivated flu vaccine in children.

Should the nasal spray flu vaccine be given to patients with chronic diseases?

Nasal spray flu vaccine is not recommended for use in people with some  chronic health conditions because the safety and effectiveness of this vaccine in people with those conditions has not been established.

Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices has a list of contraindications and precautions for the nasal spray vaccine.

Should pregnant and postpartum people avoid contact with people who  recently got the nasal spray vaccine?

Pregnant and postpartum  people do not need to avoid contact with people who recently got the nasal spray flu vaccine. However, the nasal spray flu vaccine should not be given to people who are pregnant. People who have recently had a baby can get a flu shot or the nasal spray flu vaccine.

Are there any contraindications to giving breastfeeding people the nasal spray vaccine?

Breastfeeding is not a contraindication for the nasal spray vaccine. Breastfeeding people younger than 50 years can get the nasal spray flu vaccine as long as they do not have a contraindication to getting that vaccine. Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices has a list of contraindications and precautions for the nasal spray vaccine.

Can the nasal spray flu vaccine be given to patients when they are ill?

The nasal spray flu vaccine can be given to people with mild illnesses (e.g., diarrhea or mild upper respiratory tract infection with or without fever). However, nasal congestion might limit delivery of the vaccine to the nasal lining, and so delaying vaccination until the nasal congestion is reduced or using an age-appropriate injectable vaccine instead should be considered. People with moderate or severe illness, with or without fever, should generally wait to be vaccinated until they have recovered. Your health care provider can provide advice about when to get vaccinated if you are feeling ill.

Can nasal spray flu vaccine give me flu?

Flu vaccines do not cause flu illness. The nasal spray flu vaccine contains weakened (attenuated) viruses, so that they will not cause flu illness. The weakened viruses are cold-adapted, which means they are designed to only multiply at the cooler temperatures found within the nose, and not the lungs or other areas where warmer temperatures exist.

What are the side effects that could occur with the nasal spray flu vaccine?

In children, side effects from the nasal spray may include:

• Runny nose
• Wheezing
• Headache
• Vomiting
• Muscle aches
• Fever (low grade)
• Sore throat (in older children)

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

• Runny nose
• Headache
• Cough

If these problems occur, they begin soon after vaccination and usually are mild and short-lived. People sometimes faint after medical procedures, including vaccination. Tell your provider if you feel dizzy or have vision changes or ringing in the ears. Rarely, people can experience a severe allergic reaction after a flu vaccine (or any vaccine); there are about 1-2 cases of severe allergic reactions per million flu vaccine doses administered and these reactions can be treated with medication. People who think that they have been injured by a flu vaccine can file a report with the Vaccine Adverse Event Reporting System (VAERS).

What is a trivalent influenza (flu) vaccine?

Trivalent flu vaccines protect against three different influenza viruses. Trivalent flu vaccines in the United States will include vaccine viruses or viral proteins from one influenza A(H1N1) virus, one influenza A(H3N2) virus, and one influenza B/Victoria lineage virus.

What is the difference between quadrivalent and trivalent flu vaccines?

Quadrivalent flu vaccines include vaccine viruses or viral proteins from four viruses: one influenza A(H1N1) virus, one influenza A(H3N2) virus, one influenza B/Victoria lineage virus and one B/Yamagata lineage virus. Trivalent flu vaccines include three vaccine viruses. They will not include an influenza B/Yamagata lineage vaccine virus or viral protein component.

Why is the United States transitioning from quadrivalent to trivalent flu vaccines?

The influenza B/Yamagata vaccine component in flu vaccines is being removed because influenza B/Yamagata viruses have not been detected after March 2020, using global surveillance for actively circulating influenza viruses.

What is the timeline of the transition from quadrivalent to trivalent flu vaccines?

All U.S. flu vaccines will be trivalent for the 2024-2025 season.

Has the United States had trivalent flu vaccines in the past?

Yes. Flu vaccines have been used for more than 50 years in the United States. The composition of U.S. flu vaccines is reviewed annually, and changes for most seasons. Over the years, the number of flu vaccine virus components has varied in U.S. flu vaccines, but U.S. seasonal flu vaccines were trivalent from 1978-1979 through 2012-2013. During those 35 seasons, flu vaccines included three components: one influenza A(H1N1) virus, one influenza A(H3N2) virus, and one influenza B virus (either from the B/Yamagata or B/Victoria lineage).

Why did the United States transition from trivalent to quadrivalent flu vaccines?

The U.S. transitioned to quadrivalent flu vaccines during the 2013-2014 flu season. This was done to incorporate a fourth component—a second influenza B virus—in U.S. flu vaccines to protect against both lineages of influenza B viruses (B/Yamagata lineage and B/Victoria lineage). At the time, both lineages of B viruses were circulating in people, and data indicated there was little cross-protection between the two lineages of B viruses. That meant that vaccination against one lineage of B virus would not protect against the other lineage. By the 2021-2022 flu season, all flu vaccines available in the United States were quadrivalent. However, because influenza B/Yamagata lineage viruses have not been detected after March 2020, the World Health Organization (WHO) and FDA’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) recommended that the influenza B/Yamagata lineage vaccine virus component be excluded from flu vaccines as soon as possible. During the March 2024 FDA VRBPAC meeting, FDA announced that only trivalent flu vaccines would be available for use in the United States for the 2024-2025 flu season.

Who can get trivalent flu vaccine?

All flu vaccines for use in the United States for the 2024-2025 season will be trivalent. Everyone 6 months and older should get an annual flu vaccine, but different vaccines are approved for different age groups.

Who shouldn’t get trivalent flu vaccine?

There is no specific contraindication for flu vaccine based on the number of components in the vaccine; however, different flu vaccines are approved for use in people in different age groups. In addition, some flu vaccines are not recommended for certain groups of people. Factors that can determine a person’s suitability for flu vaccine include a person’s age and health status. More information is available at Who Should and Who Should NOT get a flu vaccine.

How much trivalent flu vaccine will be available for the United States during the 2024-2025 flu season?

All flu vaccines for the 2024-2025 season are anticipated to be trivalent in the United States. Projections on U.S. flu vaccine supply for the upcoming season will come from flu vaccine manufacturers at a later time.

Are trivalent flu vaccines safe?

Yes. Trivalent U.S. flu vaccines used from 1978-1979 through 2012-2013 had an excellent safety record. There are no safety concerns regarding the transition from quadrivalent vaccines back to trivalent flu vaccines. However, as always, flu vaccines will be monitored closely for safety and effectiveness.

Background on the removal of the B/Yamagata lineage vaccine component

When was the last time that B/Yamagata lineage influenza viruses were detected, and are there risks of infection currently?

CDC and global influenza virus surveillance data show that B/Yamagata lineage influenza viruses have not been detected after March 2020. Because B/Yamagata viruses are not actively circulating in people, the risk of infection with B/Yamagata lineage viruses is considered to be low at this time. A variety of data and criteria were used to make the vaccine recommendations. More information is available at Recommended composition of influenza virus vaccines for use in the 2024-2025 northern hemisphere influenza season.

Are influenza B/Yamagata lineage viruses now extinct?

There have been no confirmed detections of influenza B/Yamagata lineage viruses after March 2020. Reports of B/Yamagata detections after March 2020 with available samples were confirmed as naturally occurring B/Victoria lineage viruses or were identified as the B/Yamagata lineage component of live attenuated vaccines (i.e., nasal spray flu vaccines). However, it is not known whether influenza B/Yamagata lineage viruses are extinct at this time.

The Global Influenza Surveillance and Response System (GISRS), a global system of public health institutions coordinated by WHO, will continue to conduct targeted surveillance for influenza B/Yamagata lineage viruses.

What happens if B/Yamagata viruses return after the component is removed from the vaccine?

Flu viruses are always changing. This is the main reason why the composition of flu vaccines is assessed annually and is updated for most seasons. CDC and WHO will continue to actively conduct targeted surveillance for influenza B/Yamagata lineage viruses. If the situation changes, CDC, FDA, and flu vaccine manufacturers will adapt accordingly. However, since there have been no confirmed actively circulating influenza B/Yamagata viruses in global surveillance after March 2020, the inclusion of a B/Yamagata antigen is no longer warranted at this time.

Brand names: AFLURIA Quadrivalent, Fluarix Quadrivalent, FluLaval Quadrivalent, Flucelvax Quadrivalent and Fluzone Quadrivalent, FluMist Quadrivalent

What is quadrivalent flu vaccine?

A quadrivalent influenza (flu) vaccine is designed to protect against four different flu viruses, including two influenza A viruses and two influenza B viruses.

Why was quadrivalent flu vaccine developed?

For many years, flu vaccines were designed to protect against three different flu viruses: an influenza A(H1N1) virus, an influenza A(H3N2) virus and one influenza B virus, even though there are two different lineages of B viruses that circulate during most seasons. Adding a B virus from the second lineage was done to give broader protection against circulating flu viruses.

Who can get quadrivalent flu vaccine?

All flu vaccines in the United States are quadrivalent. Different vaccines are approved for different age groups.

Who shouldn’t get quadrivalent flu vaccine?

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.

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.

How much quadrivalent flu vaccine will be available for the United States during the 2022-2023 flu season?

All flu vaccine for the 2022-2023 season is quadrivalent.

Are quadrivalent flu vaccines safe?

Yes. Flu vaccines that protect against four flu viruses have a safety profile similar to seasonal flu vaccines made to protect against three viruses, with similar—mostly mild—side effects. Like all seasonal flu vaccines, vaccines that protect against four flu viruses are monitored annually for their safety and effectiveness.

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.

What is Fluzone High-Dose Quadrivalent vaccine?

Fluzone High-Dose Quadrivalent vaccine contains four times the antigen as standard dose flu vaccines. It is manufactured by Sanofi Pasteur Inc. Fluzone High-Dose Quadrivalent is a four-component flu vaccine. It is one of three influenza vaccines (along with Flublok Quadrivalent and Fluad Quadrivalent) that is preferentially recommended for people 65 years and older. This preferential recommendation is new for the 2022-2023 season.

Who can receive Fluzone High-Dose Quadrivalent?

In the United States, Fluzone High-Dose Quadrivalent vaccine is approved only for people 65 years and older. Fluzone High-Dose Quadrivalent is not approved for people younger than 65 years or for people of any age with a history of severe allergic reaction to any influenza vaccine or to vaccine components other than eggs. Information about vaccine ingredients is located in the manufacturer’s package insert.

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.

What is the difference between Fluzone High-Dose Quadrivalent and Fluzone Quadrivalent?

Fluzone High-Dose Quadrivalent contains four times the antigen, the part of the vaccine that helps your body build up protection against flu viruses, than Fluzone Quadrivalent and other standard-dose inactivated flu vaccines. The higher dose of antigen in the vaccine is intended to give people 65 years and older a better immune response to vaccination, and therefore, better protection against flu. Both Fluzone High-Dose and Fluzone Quadrivalent (standard dose) are produced by the same manufacturer and are quadrivalent vaccines. There are a number of other flu vaccines produced by other manufacturers.

Are there benefits of Fluzone High-Dose Quadrivalent compared to standard dose seasonal flu vaccines for adults 65 years and older?

Data from immunogenicity studies comparing Fluzone (a trivalent standard dose vaccine) to Fluzone High-Dose (a previously available trivalent high-dose vaccine) among people 65 years and older indicated that a stronger immune response (i.e., higher antibody levels) occurred after vaccination with Fluzone High-Dose. A randomized efficacy study published in the New England Journal of Medicine indicated that the trivalent high-dose vaccine was 24% more effective in preventing flu in adults 65 years and older relative to a standard-dose vaccine.

Does Fluzone High-Dose Quadrivalent offer better protection than the adjuvanted flu vaccine?

There are currently no randomized studies comparing the efficacy of high-dose and adjuvanted influenza vaccines against laboratory-confirmed influenza. Observational studies comparing each of these vaccines suggest that each is potentially more effective in preventing influenza-associated hospitalizations (with the most data being available for the high-dose vaccine). But, the magnitude of the relative effectiveness varies with the study and season, making it difficult to conclude that one vaccine is consistently more effective than the other across multiple seasons. Of note, there are not yet studies comparing the efficacy or effectiveness of the currently available quadrivalent formulations of the high-dose and adjuvanted inactivated vaccines with standard-dose unadjuvanted vaccines. Currently available data comes from studies of the trivalent formulations of both of these vaccines.

How safe is Fluzone High-Dose Quadrivalent?

Some side effects were reported more frequently after vaccination with trivalent Fluzone High-Dose than after standard-dose inactivated flu vaccines. The most common side effects experienced during clinical studies were mild and temporary, and included pain, redness at the injection site, headache, muscle aches, and malaise. Most of these were mild in severity. In a study comparing Fluzone High-Dose Quadrivalent with trivalent Fluzone High-Dose, some of these side effect were slightly more common with the quadrivalent vaccine, but most were mild and resolved within a few days.

Does CDC recommend one vaccine above another for people 65 years and older?

The CDC and its Advisory Committee on Immunization Practices (ACIP) have not expressed a preference for any flu vaccine indicated for people 65 years and older.

What other flu vaccines are available for people 65 years and older?

All flu vaccines available for the 2022-2023 season (with the exception of the live attenuated influenza vaccine, which is approved for ages 2 through 49 years) can be used for people aged 65 years and older. However, three specific vaccines are preferentially recommended for this age group. In addition to Fluzone High-Dose Quadrivalent, one other flu vaccine is licensed specifically for people 65 years and older. This is Fluad Quadrivalent, which contains an adjuvant, an ingredient intended to help improve immune response. Additionally, there is a recombinant influenza vaccine, Flublok Quadrivalent, which was first licensed by the FDA in the United States for use in adults 18 years and older. Fluzone High-Dose Quadrivalent, Fluad Quadrivalent, and Flublok Quadrivalent are all preferentially recommended for people aged 65 years and older.

Why is there a need for flu vaccines designed specifically for people 65 years and older?

People 65 years and older are at increased risk of developing serious complications from flu compared with young, healthy adults. This is partly because human immune defenses become weaker with increasing age. During most seasons, people 65 years and older account for the majority of flu hospitalizations and deaths. In the United States, between about 70 percent and 85 percent of seasonal flu-related deaths and between 50 percent and 70 percent of seasonal flu-related hospitalizations have occurred among people 65 years and older. The weakened immune system can also mean that older people don’t respond as well to flu vaccination. Given the higher risk of severe flu illness and lower protective immune response after vaccination among older adults, substantial research and development have led to the production of new flu vaccines, including Fluzone High-Dose Quadrivalent vaccine, Flublok Quadrivalent recombinant vaccine, and Fluad Quadrivalent vaccine that potentially provide better immunity in this age group.

Flu Vaccine with Adjuvant, brand names Fluad and Fluad Quadrivalent.

What is Fluad Quadrivalent?

Fluad Quadrivalent is a standard-dose, inactivated influenza (flu) vaccine, manufactured by Seqirus that contains an adjuvant.
Fluad Quadrivalent is manufactured using an egg-based process (like most flu vaccines) and includes an adjuvant called MF59. An adjuvant is an ingredient added to a vaccine that helps create a stronger immune response to vaccination. Fluad Quadrivalent is approved for use among people 65 years and older, who often have a lower protective immune response after flu vaccination compared to younger people.

What is MF59?

MF59 is an oil-in-water emulsion of squalene oil. Squalene, a naturally occurring substance found in humans, animals, and plants, is highly purified for the vaccine manufacturing process.

Why are adjuvants added to flu vaccines?

An adjuvant is an ingredient of some vaccines that helps promote a better immune response. Adjuvants also can reduce the amount of virus needed for production of a vaccine, which can allow for greater supplies of vaccine to be manufactured.

Is Fluad Quadrivalent approved in other countries, besides the U.S.?

Fluad was initially approved in Italy in 1997, and at the time of its U.S. approval in November 2015, had been licensed in 38 countries, including Canada and 15 European countries. Fluad Quadrivalent was approved in the United States in 2020; it has been available since the 2020-2021 flu season.

Who can receive Fluad Quadrivalent?

In the United States, Fluad Quadrivalent is licensed only for people 65 years and older. FLUAD Quadrivalent should not be given to people with a history of severe allergic reaction to any flu vaccine or to vaccine ingredients other than eggs. Information about vaccine ingredients is located in package inserts from each manufacturer.

Are there benefits of Fluad Quadrivalent compared to standard-dose flu vaccines without adjuvant for adults 65 years and older?

Studies that have tested trivalent Fluad’s (a previously available, 3-component MF59-adjuvanted vaccine) ability to generate an immune response against flu viruses (immunogenicity) found that antibody levels were comparable to levels induced by a standard-dose, egg-based vaccine without adjuvant. Recent observational studies among Medicare beneficiaries 65 years and older found that trivalent Fluad provided greater protection against flu-related hospitalizations and emergency department visits than unadjuvanted standard-dose, egg-based quadrivalent flu vaccine. Another study published in Clinical Infectious Diseases among people aged 65 years and older residing in nursing homes noted that use of Fluad was associated with a lower risk of hospitalization for pneumonia and influenza compared with standard-dose influenza vaccine. Data comparing the effectiveness of Fluad Quadrivalent with standard-dose unadjuvanted inactivated vaccines are not yet available. If you have questions about which vaccine is best for you, talk to your doctor or other health care professional.

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.

How safe is Fluad Quadrivalent?

Some adverse events (which are also reported after regular flu vaccines) were reported more frequently after vaccination with Fluad than with unadjuvanted flu vaccines. The most common adverse events experienced during clinical studies were mild to moderate and were temporary, and included pain, redness at the injection site, headache, muscle aches, and malaise. In a study comparing Fluad Quadrivalent with trivalent Fluad, some of these events were slightly more common with the quadrivalent vaccine, but most were mild and resolved within a few days.

Why is there a need for flu vaccines designed specifically for people 65 years and older?

People 65 years and older are at higher risk for flu-related severe illness and death. CDC research indicates that people 65 years and older account for 70 to 85 percent of flu-related deaths and 50 to 70 percent of flu-related hospitalizations each flu season. Older adults can have lower protective immune responses after flu vaccination compared to healthy young people. Lower immune responses may lead to lower vaccine effectiveness (i.e., a measure of how well the flu vaccine protects). Given the higher risk of severe flu illness and lower protective immune response after vaccination among older adults, substantial research and development have produced new flu vaccines intended to provide better protection for people in this age group.

Brand name: Flucelvax Quadrivalent

What are cell-based flu vaccines?

‘Cell-based’ refers to how the influenza (flu) vaccine is made. Most inactivated flu vaccines are produced by growing flu viruses in eggs. The flu viruses used in the cell-based vaccines are grown in cultured cells of mammalian origin instead of in hen’s eggs.

Flucelvax Quadrivalent is the only influenza vaccine in use in the United States for which the vaccine viruses are grown in a cultured. Currently, the recombinant flu vaccine and the cell culture-based flu vaccine are the only egg-free flu vaccines licensed for use in the United States.

Who can get Flucelvax Quadrivalent?

Flucelvax Quadrivalent is licensed for use in people 6 months and older.

Why has a cell-based flu vaccine been developed?

Cell-based flu vaccine production does not use flu viruses grown in eggs and, therefore, is not dependent on the supply of eggs. In addition, use of cell-based candidate vaccine viruses (CVVs) in vaccine production has the potential to offer better protection compared to traditional, egg-based flu vaccines. The viruses used to make cell-based vaccines may be more similar to circulating “wild” flu viruses than the viruses grown in eggs and used to make egg-based vaccines. In one study published in the Journal of Infectious Diseases among Medicare beneficiaries 65 years and older during the 2017-18 influenza season, cell-based vaccine provided greater protection against flu-related hospitalizations than standard-dose, egg-based vaccine.

For the 2022-2023 flu season, all four flu CVVs used in the Flucelvax Quadrivalent are cell-based, making the vaccine egg-free.

How is the cell-based vaccine manufacturing process different than the traditional egg-based manufacturing process?

The cell-based vaccine manufacturing process uses mammalian cells (Madin-Darby Canine Kidney, or MDCK cells) to grow flu viruses instead of fertilized hen’s eggs. For the 2022-2023 season, the CVVs provided to the cell-based vaccine manufacturer are cell-derived rather than egg-derived.

What is the significance of FDA approving cell-based candidate vaccine viruses for use in the Flucelvax Quadrivalent cell-based flu vaccines?

Growing flu viruses in eggs can introduce changes (called egg-adapted changes) that can cause differences between the viruses in the vaccine and the ones that are circulating (‘wild’). These changes may have important implications for the body’s immune response to vaccination. For example, egg-adapted changes could result in production of less effective antibodies by human immune system and this can make vaccines less effective at preventing disease caused by the specific flu viruses in circulation. FDA’s approval of cell-based CVVs for use in cell-based flu vaccines could possibly improve the effectiveness of cell-based flu vaccines.

What are the possible benefits of using cell-based flu vaccines?

Some observational studies have shown greater protection against flu or flu-like illness among people who received cell-based inactivated influenza vaccines compared with those who received standard-dose egg-based inactivated vaccines.

A potential advantage of cell-based technology is that it might permit faster start-up of the vaccine manufacturing process in the event of a pandemic. The cells used to manufacture Flucelvax Quadrivalent are kept frozen and “banked.” Cell banking ensures an adequate supply of cells is readily available for vaccine production. Growing CVVs in cell culture for the manufacture of Flucelvax Quadrivalent is not dependent on an egg supply. Cell-based vaccines might be easier to scale up when egg supply is limited.

What were the results of the clinical trials using cell-based technology?

A clinical trial of the previous trivalent formulation of Flucelvax demonstrated effectiveness and safety among persons 18 through 49 years old. In immunogenicity studies among people 18 years and older and 4 through 17 years old, Flucelvax Quadrivalent was found to produce a similar immune response to the trivalent formulation. Post-vaccination symptoms were typical of those seen with other injectable flu vaccines. Flucelvax Quadrivalent was subsequently studied in younger children, and as of October 2021 it is approved for persons 6 months of age and older.

Has cell-based technology been used before?

Cell culture technology has been used to produce other U.S.-licensed vaccines, including vaccines for rotavirus, polio, smallpox, hepatitis, rubella and chickenpox.

Cell-based flu vaccines have been approved for use in many European countries.

What is Recombinant Flu Vaccine?

Recombinant influenza (flu) vaccines are produced using recombinant technology. This method does not require an egg-grown vaccine virus and does not use chicken eggs in the production process.

Recombinant flu vaccine was first licensed by the FDA in the United States in 2013. Currently, the recombinant flu vaccine and the cell culture-based flu vaccine are the only egg-free flu vaccines licensed for use in the United States.

There is one quadrivalent recombinant flu shot (Flublok Quadrivalent) available for the 2022–2023 influenza season.

How does Recombinant flu vaccine differ from the other approved flu vaccines?

Recombinant flu vaccines do not use the flu virus or chicken eggs in the manufacturing process.

Who can get Flublok Quadrivalent?

Flublok Quadrivalent is licensed for use in people 18 years and older.

Who should not get Flublok Quadrivalent?

People who are not within the FDA-approved age range (those younger than 18 years) and who have had severe allergic reactions to any ingredient of the vaccine should not get Flublok Quadrivalent.

What are the possible benefits of recombinant flu vaccines?

Recombinant flu vaccine (brand name: Flublok Quadrivalent) is one of the three vaccines that are preferentially recommended for people 65 years and older because a review of existing studies suggested that, in this age group, these vaccines are potentially more effective than standard dose unadjuvanted flu vaccines. Other possible benefits of recombinant vaccine include that this vaccine technology is not dependent on an egg supply so the manufacturing process might be faster than that of egg-based vaccines in the event of a pandemic or shortage of the eggs needed to grow influenza viruses. This process is not limited by the selection of vaccine viruses that are adapted for growth in eggs. It also avoids mutations that can occur when viruses are grown in eggs, which can sometimes affect how well the finished vaccine works.

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.

Is this vaccine safe? Are there any side effects that could occur?

In clinical studies, the safety of recombinant flu vaccines was comparable to that of other injectable flu vaccines.  The most common side effects reported after receipt of Flublok Quadrivalent were similar to those reported for other injectable vaccines and include pain and tenderness at the injection site, headache, fatigue, and muscle or joint aches.

Special Consideration Regarding Egg Allergy

People with egg allergies can receive any licensed, recommended age-appropriate influenza (flu) 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.

What is a jet injector and how is it used for vaccination?

A jet injector is a medical device used for vaccination that uses a high-pressure, narrow stream of fluid to penetrate the skin instead of a needle. Jet injectors may be powered by compressed gas or springs. The devices were invented in the 1960s and were used successfully in mass vaccination efforts to prevent smallpox and other diseases. In the past, the devices were often used to vaccinate members of the armed forces.

What flu vaccines are available via jet injector this season?

One flu vaccine, AFLURIA Quadrivalent^®, is approved for use with a jet injector this season. AFLURIA Quadrivalent^® (i.e., four ingredient) flu vaccine provides protection against an influenza A(H1N1) virus, and influenza A(H3N2) virus and two influenza B viruses.

Who can be vaccinated with flu vaccine administered by jet injector?

Flu vaccination with AFLURIA Quadrivalent^® via jet injector is approved for use in people aged 18 through 64. AFLURIA Quadrivalent also may be given by needle and syringe, for people 6 months old and older.

How effective is flu vaccine administered by jet injector?

Clinical trial data used in FDA’s approval of the jet injector (i.e., the PharmaJet Stratis Needle-Free Injector used with the previous trivalent AFLURIA^®) demonstrated that vaccination using this jet injector method provided a non-inferior (i.e., similar) level of immune protection compared to the same flu vaccine administered via traditional flu shot.

What side effects are associated with flu vaccination administered via jet injection?

In adults 18 through 64 years, the most common injection-site reactions observed in a clinical study of the jet injector flu vaccine up to 7 days post-vaccination were tenderness, swelling, pain, redness, itching and bruising. The most common side effects within this period were myalgia (muscle pain), malaise (i.e., the feeling of discomfort or unease like when you are first getting sick), and headache.

Does flu vaccine administered by jet injector contain thimerosal?

Yes. The Afluria Quadrivalent® formulation used for administration by jet injector comes in multi-dose vials, which contain thimerosal.

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.