ACOG Influenza FAQs for Providers

Should pregnant women be immunized against seasonal influenza (flu)?

Yes. Influenza vaccination is an essential element of prenatal care because pregnant women are at increased risk for serious illness and mortality due to influenza. Case reports and limited studies indicate that pregnancy can increase the risk for serious medical complications of influenza. One study found that during an average flu season, 25 of every 10,000 women in their third trimester of pregnancy will be hospitalized for flu-related complications. In addition, maternal immunity is the only effective strategy for newborns because the vaccine is not approved for use in infants younger than 6 months.

Is it safe for pregnant women to be immunized against seasonal influenza?

Yes. There is no study to date that has shown an adverse consequence for women or their offspring following administration of inactivated influenza vaccine to pregnant women.  The influenza vaccine is made the same way each year, with the only difference being the use of a different strain of influenza. There have been no reports of any adverse outcomes in pregnant women or their infants. 

During which trimester should pregnant women be immunized?

All women who will be pregnant during influenza season (October through May) should receive inactivated influenza vaccine at any point in gestation.

Which flu vaccine should pregnant women receive?

Pregnant women should receive the inactivated influenza vaccine that is injected intramuscularly in the deltoid. Currently, there are two types that are available: The trivalent or quadrivalent vaccines may be used during pregnancy. The Advisory Committee on Immunization Practices (ACIP) and ACOG do not preferentially recommend a specific formulation––trivalent or quadrivalent––of the influenza vaccine.  Live attenuated influenza vaccine is contraindicated for pregnant women.

Is it safe for pregnant women to receive an influenza vaccine that contains mercury (thimerosal)?

Yes. Thimerosal, a mercury-containing preservative used in multidose vials, has not been shown to cause any adverse effects except for occasional local skin reactions. There is no scientific evidence that thimerosal-containing vaccines cause adverse effects including autism in children born to women who received vaccines with thimerosal.

A study of influenza vaccination examining over 2,000 pregnant women demonstrated no adverse fetal effects associated with the influenza vaccine.

Additionally, excess influenza-associated deaths among pregnant women have been documented during influenza pandemics. Because pregnant women are at increased risk for influenza-related complications and because a substantial safety margin has been incorporated into the health guidance values for organic mercury exposure, the benefits of influenza vaccine with reduced or standard thimerosal content outweigh the theoretical risk, if any, of thimerosal.

Should we provide antiviral chemoprophylaxis to pregnant women exposed to influenza?

Yes. Due to the high potential for morbidity in pregnant and postpartum patients, the CDC recommends that post-exposure antiviral chemoprophylaxis can be considered for pregnant women and women who are up to 2 weeks postpartum (including following pregnancy loss) who have had close contact with someone likely to have been infectious with influenza. Chemoprophylaxis is Oseltamivir 75 mg QD for 10 days.

All women who are pregnant or in the first two weeks after delivery or pregnancy loss should be counseled about the early signs and symptoms of influenza infection such as fever over 100.0º F coupled with difficulty breathing, dizziness when standing, or pain in the chest and advised to immediately call for evaluation if clinical signs or symptoms develop.  

For more information on antiviral chemoprophylaxis in pregnant and postpartum women see the CDC website:

For more information visit CDC's section concerning Seasonal Flu Vaccine Safety and Pregnant Women





Updated 10/22/15

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