Questions & Answers

Seasonal Flu Vaccine Safety and Pregnant Women

Influenza is more likely to cause severe illness in pregnant women than in women who are not pregnant. Changes in the immune system, heart, and lungs during pregnancy make pregnant women more prone to severe illness from influenza as well as hospitalizations and even death. Pregnant women with influenza also have a greater chance for serious problems for their unborn babies, including premature labor and delivery.

Why should pregnant women get the seasonal flu vaccine?

Pregnant women have a higher risk for serious complications from influenza than non-pregnant women of reproductive age. Influenza vaccine will protect pregnant women, their unborn babies, and protect the baby after birth.

To prevent influenza and complications in pregnant women, the Centers for Disease Control and Preventiona??s (CDC) Advisory Committee on Immunization Practices (ACIP) in 2004 began recommending routine immunization of pregnant women with the flu shot at any stage of pregnancy. The nasal spray vaccine is not recommended for use in pregnant women.

ACIP recommendations for influenza vaccination during the 2010-11 season can be found at: http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5908a1.htm. 

Is it safe for pregnant women to get seasonal flu vaccine?

Yes. The seasonal flu shot has been given safely to millions of pregnant women over many years. Flu shots have not been shown to cause harm to pregnant women or their babies.

What research shows that seasonal flu vaccine is safe for unborn babies?

Studies of several thousand pregnant women in scientific literature have assessed the safety of using the flu vaccine during pregnancy. These studies have shown no evidence of harm to pregnant women, to the unborn child (or fetus) or to newborns of vaccinated women. In addition, the Food and Drug Administrationa??s (FDA) and CDCa??s routine monitoring of adverse events has not raised safety concerns.

What side effects have pregnant women experienced from the seasonal flu shot?

The most common side effects after flu shots are mild, such as being sore and tender and/or red and swollen where the shot was given. Some people might have headache, muscle aches, fever, and nausea or feel tired. If these problems happen, they usually begin soon after the shot is given and may last as long as 1-2 days. Some people may faint after getting any shot. Sometimes, flu shots can cause serious problems like severe allergic reactions. But, life-threatening allergic reactions to vaccines are very rare. A person who has a severe (life-threatening) allergy to eggs or to anything else in the vaccine should not get the shot, even if she is pregnant. Pregnant women 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.

What studies has CDC conducted on adverse events in pregnant women who received seasonal flu vaccine?

CDC, in collaboration with FDA, recently conducted a search of reports to the Vaccine Adverse Events Reporting System (VAERS) of pregnant women who received seasonal influenza vaccines from 1990 to 2009 to assess potential vaccine safety concerns. Theresults of this study were recently published in the American Journal of Obstetrics and Gynecology.

Overall, the study concluded that no unusual patterns of pregnancy complications or adverse fetal outcomes were observed in the VAERS reports of pregnant women after being given the flu shot or nasal spray flu vaccine (while the nasal spray is not recommended for pregnant women, scientists were reassured to find that the inadvertent administration of this vaccine to pregnant women did not result in reported unexpected reactions). Data from CDC's 19-year review of VAERS add to an existing body of evidence supporting the safety of the flu shot for pregnant women. CDC is also conducting studies of flu vaccine safety through the Vaccine Safety Datalink (VSD) Project.

What do studies show about pregnant women and the safety of last yeara??s 2009 H1N1 flu vaccine?

Considerable efforts were made to study the safety of vaccinating pregnant women with the 2009 H1N1 flu vaccine during the 2009-2010 flu season. CDCa??s Immunization Safety Office, in collaboration with FDA, conducted a review of the VAERS database from October 1, 2009 to June 30, 2010 of pregnant women who received 2009 H1N1 flu vaccine. The review found no unexpected or unusual adverse events.

The search found a total of 344 reports, of which 149 (43.3%) were reports of spontaneous abortion and 21 (6.1%) were reports of stillbirths. Of these reports, 105 (30.5%) spontaneous abortions and 18 (5.2%) stillbirths were verified by review of medical records. The reporting rates for spontaneous abortions and stillbirths were 49.6 and 7.4 reports per one million pregnant women vaccinated, respectively.

About 10.4% - 22.4% of all pregnancies end in spontaneous abortion and almost 0.5% of all pregnancies end in stillbirths regardless of vaccination. Thus, reporting rates to VAERS for spontaneous abortions and stillbirths were well below the normal rates that are expected in the general population. The studies show there was no increase in adverse events in pregnant vaccinated women than in non-vaccinated women.

How is the safety of the 2010-2011 seasonal flu vaccine being monitored?

As part of its influenza vaccine monitoring activities, CDC and FDA are monitoring the safety of seasonal influenza and other vaccines licensed for use in the United States, in cooperation with state and local health departments, health care providers, and other partners. Monitoring the safety of flu vaccine in pregnant women is part of this effort.

Two main systems being used to monitor flu vaccine safety are VAERS, which is jointly operated with FDA, and the Vaccine Safety Datalink (VSD) Project, managed and coordinated by CDCa??s Immunization Safety Office. Other systems are also being used. Through vaccine safety monitoring, CDC and FDA are able to quickly identify any clinically significant adverse events following immunization that warrant further study or action to protect the health of the public.

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