Influenza Vaccine Safety Considerations for People Who Are Pregnant or Breastfeeding

Background

Influenza is more likely to cause illness that results in hospitalization in pregnant people than in people of reproductive age who are not pregnant. Influenza also may be harmful for the developing baby. A common influenza sign can be fever, which has been associated in some studies with neural tube defects and other adverse outcomes for a developing baby. Getting vaccinated while pregnant can also help protect a baby from influenza after birth (because antibodies are passed from the pregnant parent to the developing baby during pregnancy). People who get the influenza vaccine while pregnant or breastfeeding also develop antibodies against influenza that they can share with their infants through their breast milk.

An Influenza Vaccine Is the Best Protection Against Influenza

Getting an influenza vaccine is the first and most important action a person can take to protect against influenza and its potentially serious complications. Pregnant people should get an injectable influenza vaccine (shot) and not the nasal spray influenza vaccine. A 2013 study showed that during the 2010–2011 and 2011–2012 influenza seasons vaccination reduced the risk of influenza in pregnant people by up to 50%. These results are consistent with the general range of estimated influenza vaccine effectiveness among adults 18-64 years. A 2018 study showed that getting an influenza shot reduced a pregnant person's risk of being hospitalized with influenza by an average of 40%. Pregnant people who get an influenza shot are also helping to protect their babies from influenza illness for the first several months after their birth, when they are too young to get vaccinated. A list of recent studies is available at benefits of influenza vaccination for pregnant people. September and October are generally good times to be vaccinated each year. Early vaccination during July and August also can be considered for people who are in the third trimester of pregnancy during those months.

The CDC's Advisory Committee on Immunization Practices and the American College of Obstetricians and Gynecologists recommend that all adults receive an annual influenza vaccine and that people who are or will be pregnant during influenza season receive an inactivated influenza vaccine (pregnant people should not receive a live attenuated influenza vaccine) as soon as it is available. Millions of doses of influenza vaccines have been administered safely for more than 50 years, including to pregnant people. The safety of influenza vaccination during pregnancy has been consistently demonstrated by numerous clinical trials, observational studies, and data from safety reporting systems.

Getting an Influenza Vaccine While Pregnant Does Not Increase the Risk of Miscarriage or Stillbirth

CDC's Vaccine Safety Datalink (VSD) project conducted one of the largest studies examining influenza vaccination and risk of miscarriage. The study covered three influenza seasons (2012–2013, 2013–2014, 2014–2015), looking for any increased risk for miscarriage among those who had received an influenza vaccine during their pregnancy. The study found no increased risk of miscarriage associated with influenza vaccination during pregnancy. This study was a follow-up to a previous smaller study that suggested pregnant people who received H1N1-containing influenza vaccine two years in a row might have an increased risk of miscarriage. The more recent results from this larger study showed that influenza vaccination was safe for pregnant people and their unborn babies and support the current ACIP recommendation for influenza vaccination at any time during pregnancy. Another study in the VSD (Panagiotakopoulos et al. 2020) examined the risk of stillbirths (fetal deaths occurring after 20 weeks gestation) among pregnant women who received an influenza vaccine and found no increased risk of this event among influenza vaccine recipients.

Studies

Earlier Studies That Support the Safety of Influenza Vaccination in Pregnant People include:

1. Reviews of reports to the Vaccine Adverse Event Reporting System(VAERS) (Moro et al, 2011and Moro et al, 2017 found no unusual or unexpected patterns of pregnancy complications or adverse fetal outcomes associated with influenza vaccines.
2. A study using VSD data (Irving et al, 2013) found no increased risk of miscarriage among pregnant people who received influenza vaccines in the 2005–06 or 2006–07 flu seasons.
3. A large study using VSD data (Kharbanda et al, 2013) found no increased risk for adverse obstetric events such as chorioamnionitis, pre-eclampsia, or gestational hypertension among pregnant people who received an influenza vaccine from 2002 to 2009 when compared to pregnant those who were not vaccinated.
4. A VSD study (Nordin et al, 2014) compared pregnant people who received an influenza vaccine during the 2004-05 and 2008-09 flu seasons with an equal number who did not. The study found that rates of premature delivery or small for gestational age infants were the same for both groups.
5. A large August 2017 study using VSD data found that the babies of people vaccinated during their first trimester had no increased risk of major birth defects.