Flu Vaccine Safety and Pregnancy

If you are pregnant, you should get a flu shot

Influenza (flu) during pregnancy is more likely to cause illness that results in hospitalization. Influenza also may be harmful for the developing baby. A common influenza sign, fever, has been associated in some studies with neural tube defects and other adverse outcomes for a developing baby. Getting vaccinated while pregnant also can help protect a baby from influenza after birth (because antibodies are passed to a developing baby during pregnancy). When you get an influenza vaccine while pregnant or breastfeeding, your body develops antibodies against influenza that are shared with your baby through breast milk.

A flu vaccine is the best protection against flu

Getting an influenza (flu) vaccine is the first and most important step to protect against flu. If you are pregnant, you should get a flu shot and not the nasal spray flu vaccine. Flu shots given during pregnancy help protect both the pregnant mother and the baby from flu. A 2013 study showed that during the 2010–2011 and 2011–2012 flu seasons vaccination reduced the risk of flu-associated acute respiratory infection during pregnancy by up to one-half. These results are consistent with the general range of estimated flu vaccine effectiveness among adults 18-64 years. A 2018 study showed that getting a flu shot during pregnancy reduced the risk of being hospitalized with flu by an average of 40%. Getting a flu vaccine during pregnancy also helps to protect babies from flu illness and flu related hospitalizations for the first several months after their birth, when they are too young to get vaccinated.

Influenza vaccine can be given during any trimester of pregnancy. September and October are generally good times to be vaccinated each year. Early flu vaccination (i.e., during July and August) can be considered during the third trimester of pregnancy if vaccine is available.

Vaccine safety during pregnancy

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 for pregnant women and their babies, and CDC continues to gather data on this topic.

Miscarriage

Multiple studies have shown that people who have received flu shots during pregnancy have not had a higher risk of spontaneous abortion (miscarriage). One of these studies was conducted using CDC's Vaccine Safety Datalink (VSD). The study covered three flu seasons (2012-13, 2013-14, 2014-15) looking for any increased risk for miscarriage among pregnant women 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 as a 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 spontaneous abortion (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 miscarriage following flu vaccination. The Advisory Committee on Immunization Practices (ACIP), the American College of Obstetricians and Gynecologists (ACOG) and CDC recommend flu vaccination during any trimester of pregnancy because flu poses a danger during pregnancy and a flu vaccine can prevent serious illness, including hospitalization, during pregnancy.

Side effects

The most common side effects from flu vaccination experienced during pregnancy 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.

Who should not get a flu shot

Anyone with a severe, life-threatening allergy to any of the ingredients or components of a particular vaccine (other than egg protein) should not get that vaccine. People who have had a severe, life-threatening allergic reaction to a previous dose of an influenza vaccine should generally not be vaccinated, depending upon what kind of influenza vaccine caused the allergic reaction. It is important to discuss allergies that you have (such as allergies to medications or vaccines and other allergies) with your health care provider.

Egg allergies

Pregnant women with egg allergies of any severity may get any flu shot (egg-based or non-egg-based) that is otherwise appropriate for their age and health status. The nasal spray flu vaccine (live attenuated influenza vaccine or LAIV) should not be used during pregnancy. 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.

Monitoring safety of flu vaccines during pregnancy

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 for health concerns (also termed "adverse events") following vaccination. Anyone can report adverse events after vaccination to VAERS. Generally, information from VAERS reports cannot determine if an adverse event after vaccination 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 13 health care organizations which monitors the safety of vaccines and conducts vaccine safety studies.

CDC studies conducted on flu vaccine during pregnancy

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

1. Review of reports to the Vaccine Adverse Reporting System (VAERS)12 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 (miscarriage) after flu vaccination during pregnancy. A similar study using VSD data 3from the 2005-06 and 2006-07 seasons also found no increased risk of miscarriage during pregnancy after receiving a flu vaccine. One study of the 2010-2012 flu seasons, however, found that women 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 data4 found no increased risk for adverse pregnancy events (like chorioamnionitis, pre-eclampsia, or gestational hypertension) for pregnant women who received the flu vaccine from 2002 to 2009 when compared to pregnant women who were not vaccinated.
4. A VSD study5compared pregnant women who received the flu shot with an equal number of pregnant women 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 women who received the flu shot during their first trimester had no increased risk of having children with major birth defects.
6. A VSD study6 examined stillbirth rates in pregnant women aged 14-49 years between 2007 and 2015 and did not find a significant association between influenza vaccination during pregnancy and stillbirth.