Influenza (flu) is more likely to cause severe illness in pregnant people than in people of reproductive age who are not pregnant. Changes in the immune system, heart, and lungs during pregnancy may make pregnant people (and people up to two weeks postpartum) more prone to severe illness from flu, including illness resulting in hospitalization. Flu also may be harmful for a pregnant person’s developing baby. A common flu symptom is fever, which may be associated with neural tube defects and other adverse outcomes for a developing baby. Getting vaccinated during pregnancy also can help protect a baby from flu during the first several months after birth (the pregnant parent passes antibodies on to the developing baby during pregnancy).

If you get flu symptoms call your health care provider right away. There are flu antiviral drugs that can treat flu illness and prevent serious flu complications. CDC recommends prompt flu antiviral treatment for people who have confirmed or suspected flu infection and who are at higher risk of serious flu complications, such as pregnant people. Early treatment of flu in hospitalized pregnant people has been shown to reduce the length of the hospital stay.

Flu symptoms include fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills, and fatigue. Some people may also have vomiting and diarrhea, though this is more common in children than in adults. People may be infected with flu and have respiratory symptoms without a fever.

A study from the Centers for Disease Control and Prevention (CDC) found thatwomen who had a cold or flu with fever just before or during early pregnancy may be more likely to have a baby born with a birth defect.

Main Findings

• Having a cold or flu with fever just before or during early pregnancy may be related to these birth defects:
  • Anencephaly
  • Spina bifida
  • Encephalocele
  • Cleft lip with or without cleft palate
  • Colonic atresia/stenosis
  • Bilateral renal agenesis/hypoplasia
  • Limb reduction defects
  • Gastroschisis

• Women who had a cold or flu without fever did not appear to have an increased chance of having a baby born with a birth defect.
• Women who are planning a pregnancy should consider taking steps to protect themselves from fever and infection during early pregnancy to help prevent birth defects.

About the Study

Researchers used data from the National Birth Defects Prevention Study (NBDPS), one of the largest U.S. studies aimed at understanding factors that increase the risk for major birth defects.

About Birth Defects

Birth defects are common, costly, and critical conditions that affect 1 in every 33 babies born in the United States each year. Birth defects are structural changes present at birth that can affect almost any part or parts of the body (such as the heart, brain, face, arms, and legs). They may affect how the body looks, works, or both.

• Influenza antiviral drugs are medicines that fight against flu by keeping flu viruses from making more viruses in your body.
• Antiviral drugs can make your flu illness milder and make you feel better faster. They may also prevent serious health problems that can result from flu illness.
• Treatment with an influenza antiviral drug should begin as soon as possible because these medications work best when started early (within 48 hours after symptoms start).
• You need a prescription from a health care provider for an influenza antiviral medication.
• There are four FDA-approved flu antiviral drugs recommended by CDC this season that can be used to treat the flu.

The Centers for Disease Control and Prevention (CDC) recommends women in any trimester of their pregnancy who have a suspected or confirmed influenza infection receive prompt antiviral therapy with Tamiflu (oseltamavir) or Relenza (zanamivir).

Are Tamiflu and Relenza safe to use in pregnancy?

Relenza and Tamiflu are both FDA approved for treatment of influenza. Both drugs have been carefully looked at to understand their safety profile in pregnancy and we are continuing to monitor them closely. For a pregnant woman and her developing baby, the benefit of any drug needs to be considered in light of the risks from the drug and the risks from not treating the disease or condition.

The CDC has looked at these issues carefully for pregnant women: because the risks of influenza for pregnant women are serious, CDC believes that the benefits of antiviral therapy outweigh the potential for risks from the drugs.

Both drugs are designated "Pregnancy Category C," which means that they have not been studied in pregnant women. However, Pregnancy Category C does NOT mean the drug cannot be used in pregnant women. Pregnant women can and should receive a category C drug when the possible benefits of using the drug are more likely than the possible risk of harm to the woman or her baby.

What else should pregnant women know?

If your doctor diagnoses influenza and prescribes Tamiflu or Relenza for you, do not wait to start the treatment. Antiviral drugs are most beneficial if treatment starts within 2 days of the start of influenza symptoms. You will probably need to take the medicine for at least 5 days.
Don’t avoid getting a flu shot. Antiviral therapy does not substitute for vaccination against seasonal and or H1N1 influenza.

If you are pregnant and have any of these signs, call 911 right away:

• Difficulty breathing or shortness of breath
• Persistent pain or pressure in the chest or abdomen
• Persistent dizziness, confusion, inability to arouse
• Seizures
• Not urinating
• Severe muscle pain
• Severe weakness or unsteadiness
• Fever or cough that improve but then return or worsen
• High fever that is not responding to Tylenol (or store brand equivalent)
• Decreased or no movement of your baby

This list is not all inclusive. Please consult your medical provider for any other symptom that is severe or concerning.

Getting a flu vaccine is the first and most important action a person can take to protect against flu and its potentially serious complications. Pregnant people should get a flu shot and not the nasal spray flu vaccine. Vaccination has been shown to reduce the risk of flu in pregnant people by up to 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%. Pregnant people who get a flu shot also are helping to protect their babies from flu illness for the first several months after their birth, when they are too young to get vaccinated.

For most people who only need one dose of flu vaccine for the season, September and October are generally good times to be vaccinated. 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 from flu for several months after birth (when they are too young to be vaccinated). Some children need two doses of flu vaccine given at least four weeks apart (children 6 months through 8 years of age who either have never received flu vaccine, or who have not already received a total of at least two doses in their lives). For those children, it is recommended to get the first dose as soon as vaccine is available, so that they can receive the second dose (which has to be given at least four weeks after the first) by the end of October.

Flu shots have been given to millions of pregnant people over many years with an excellent safety record. There is a lot of evidence that flu vaccines can be given safely during pregnancy. CDC and ACIP recommend that pregnant people get vaccinated during any trimester of their pregnancy.

Pre-Existing Conditions

There is no recommendation that pregnant people or people with pre-existing medical conditions need to get special permission or written consent from their doctor or health care professional for influenza (flu) vaccination if they get vaccinated at a worksite clinic, pharmacy, or other location outside of their physician’s office. Pregnant people should not get nasal spray vaccine.

Why should pregnant people get a flu shot?

Influenza is more likely to cause severe illness in pregnant people than in people of reproductive age who are not pregnant. Changes to the immune system, heart, and lungs during pregnancy make people more susceptible to influenza severe enough to cause hospitalization throughout pregnancy and up to two weeks postpartum. Influenza also may be harmful for the developing baby. A common influenza symptom fever may be associated with neural tube defects and other adverse outcomes for a developing baby. Parental vaccination also can help protect a baby from influenza after birth (because antibodies are passed to a developing baby during pregnancy).

A Flu Vaccine is the Best Protection Against Flu

Getting an influenza (flu) vaccine is the first and most important step in protecting against flu. Pregnant people should get a flu shot and not the nasal spray flu vaccine. Flu shots given during pregnancy help protect both the pregnant parent and the baby from flu. Vaccination has been shown to reduce the risk of flu-associated acute respiratory infection in pregnant people by up to 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 percent. Pregnant people who get a flu vaccine also are helping to protect their babies from flu illness for the first several months after their birth, when they are too young to get vaccinated. A list of recent studies on the benefits of flu vaccination for pregnant people is available.

September and October are generally good times to be vaccinated. Early vaccination also can be considered for people who are in the third trimester of pregnancy, because this can help protect the baby after birth during their first months of life (when they are too young to be vaccinated). Some children need 2 doses given at least 4 weeks apart (children 6 months through 8 years of age who either have never received flu vaccine, or who have not already received a total of at least 2 doses in their lives). These children should get their first dose soon after vaccine is available, so that they can receive the second dose (which has to be given at least 4 weeks after the first) by the end of October.

Is it safe for pregnant people and their developing babies to get a flu shot?

Yes. Flu shots have been given to millions of people over many years with an excellent safety record. There is a large body of scientific studies that supports the safety of flu vaccine in pregnant people and their babies, and CDC continues to gather data on this topic.

Can flu vaccination result in miscarriage?

Multiple studies have shown that people who have received flu shots during pregnancy have not had a higher risk for spontaneous abortion (miscarriage). One of the largest and strongest studies was conducted in CDC’s Vaccine Safety Datalink (VSD) project. The recently published study covered three flu seasons (2012-13, 2013-14, 2014-15) looking for any increased risk for miscarriage among pregnant people who had received a flu vaccine during their pregnancy. The study found NO increased risk for miscarriage after flu vaccination during pregnancy. This study was conducted in follow-up to a previous smaller study. The prior study examined data from the 2010-2011 and 2011-2012 flu seasons and identified an association between flu vaccination early in pregnancy and an increased risk of spontaneous abortion or miscarriage; particularly among people who had received flu vaccine during the previous flu season. However, the smaller study had several limitations, including small sample size which could have led to imprecise results. This study was the only analysis to show that association; no other studies had found an increased risk of SAB following flu vaccination At this time, the Advisory Committee on Immunization Practices (ACIP), the American College of Obstetricians and Gynecologists (ACOG) and CDC continue to recommend that pregnant people get a flu vaccine during any trimester of their pregnancy because flu poses a danger to pregnant people and a flu vaccine can prevent serious illness, including hospitalization, during pregnancy.

Any pregnant person who has questions about vaccines should talk to their doctor.

What side effects have pregnant people experienced from flu shots?

The most common side effects experienced by pregnant people are the same as those experienced by other people. They are generally mild and include:

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

If side effects occur, they usually begin soon after the shot is given and generally last for 1-2 days.

A flu shot, like other injections, can occasionally cause fainting. Rarely, flu shots can cause serious problems like severe allergic reactions. Anyone with a severe, life-threatening allergy to any of the vaccine ingredients should not get the shot.

Can pregnant people with egg allergies get vaccinated?

Most people who have an allergy to eggs can get vaccinated, with some additional safety measures. A person with severe (life-threatening) allergy to any vaccine component, including egg protein, should not get the shot, even if they are pregnant. Pregnant people should tell the person giving the shots if they have any severe allergies or if they have ever had a severe allergic reaction following a flu shot.

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

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 influenza viruses are circulating that season and, potentially, which type of flu vaccine was used.

How is the safety of flu vaccines in pregnant people monitored?

CDC and FDA conduct ongoing safety monitoring of vaccines licensed for use in the United States.

CDC and FDA monitor flu vaccine safety during pregnancy during each flu season using the Vaccine Adverse Event Reporting System (VAERS): An early warning system that helps CDC and FDA monitor health concerns following vaccination. Anyone can report possible vaccine side effects to VAERS. Generally, VAERS reports cannot determine if a health concern that arises after vaccination (adverse event) was caused by a vaccine, but these reports can help indicate if further investigations are needed.

In addition CDC conducts research studies in the Vaccine Safety Datalink (VSD): A collaboration between CDC and nine health care organizations which allows ongoing monitoring and proactive searches of vaccine-related data.

What studies has CDC conducted on flu vaccine safety during pregnancy?

Several studies conducted by CDC and partners support the safety of the flu vaccine for pregnant people and their babies.

1. Review of reports to the Vaccine Adverse Reporting System (VAERS) found no evidence to suggest a link between pregnancy complications or adverse fetal outcomes among pregnant women and flu shots.
2. A large study using VSD data from three flu seasons (2012-13, 2013-14, 2014-15) found no increased risk for spontaneous abortion after flu vaccination during pregnancy. A similar study using VSD data (Irving et al, 2013) from the 2005-06 and 2006-07 seasons also found no increased risk of miscarriage among pregnant people who received flu vaccines. One study of the 2010-2012 flu seasons, however, found that people in early pregnancy who received two consecutive annual flu vaccines had an increased risk of miscarriage in the 28 days after receiving the second vaccine. A limitation of this study was its small sample size which could have led to imprecise results. In response to the findings from the 2010-2012 flu season study, CDC provided funding for the larger follow-up VSD study conducted during the 2012-2015 flu seasons that included about three times as many people and found no association between flu vaccination and miscarriage.
3. A large study using VSD data (Kharbanda et al, 2013) found no increased risk for adverse obstetric events (like chorioamnionitis, pre-eclampsia, or gestational hypertension) for pregnant people who received the flu vaccine from 2002 to 2009 when compared to pregnant people who were not vaccinated.
4. A VSD study (Nordin et al, 2014) compared pregnant people who received the flu shot with an equal number of pregnant people who did not receive the flu shot during the 2004-05 and 2008-09 flu seasons. The study found no differences between the two groups in the rates of premature delivery or small for gestational age infants.
5. A large August 2017 study using VSD data found that the babies of people who received the flu shot during their first trimester had no increased risk of having children with major birth defects.

Where should a pregnant person get vaccinated?

There are many different options for pregnant people to receive a flu shot, including a health care provider’s office, at work, a pharmacy, some stores, or a supermarket. All these places give flu vaccines that are licensed and approved for use in the United States. If you’ve never had a problem when previously receiving a flu vaccine, then there is no reason you can’t get a flu vaccine at work or a supermarket.

What about thimerosal in flu vaccines? Should pregnant people get thimerosal-free flu vaccines?

Studies have shown the small amount of thimerosal in vaccines does not cause harm. There is thimerosal-free flu vaccine available for people who want to avoid thimerosal.

Can a breastfeeding person get a flu vaccine?

Yes. People who are breastfeeding should get a flu vaccine to protect themselves from flu. Getting vaccinated reduces pregnant parents’ risk of getting sick and of passing the flu on to their babies, thus protecting their babies from flu also. This is especially important for children younger than 6 months old since they are too young to receive flu vaccine themselves.