Is the flu shot safe to administer at any gestational age in pregnancy?

Influenza Vaccination Safety During Pregnancy

The influenza vaccine is safe to administer during any trimester of pregnancy and is recommended for all pregnant women regardless of gestational age. 1

Safety Profile Across All Trimesters

• Inactivated influenza vaccines (IIV) can be safely administered during any trimester of pregnancy, with substantial evidence supporting their safety throughout gestation 1
• Multiple medical organizations including the Advisory Committee on Immunization Practices (ACIP), American College of Obstetricians and Gynecologists, and American Academy of Family Physicians consistently recommend influenza vaccination during any trimester 1
• A 5-year retrospective cohort study (2003-2008) with over 10,000 women found that influenza vaccination in the first trimester was not associated with increased rates of major congenital malformations 1
• A systematic review and meta-analysis of 15 studies (14 cohort studies and 1 case-control study) showed no association between congenital defects and influenza vaccination in any trimester, including the first trimester 1

Benefits of Vaccination During Pregnancy

• Maternal influenza immunization prevents laboratory-confirmed influenza disease and complications in both mothers and their infants during the first 2-6 months of life 1
• Infants born to women who receive influenza vaccination during pregnancy have shown a risk reduction of up to 72% (95% CI, 39% to 87%) for laboratory-confirmed influenza hospitalization in the first few months of life 1
• Pregnant women are at increased risk for severe illness and complications from influenza, particularly during the second and third trimesters 1, 2
• Vaccination provides protection to infants through transplacental passage of antibodies during the first 6 months of life, when they are too young to receive influenza vaccines themselves 1

Vaccine Types and Considerations

• Any licensed, recommended, and age-appropriate inactivated influenza vaccine may be administered during pregnancy 1
• Live attenuated influenza vaccine (LAIV) is contraindicated during pregnancy but can be used postpartum 1
• Experience with recombinant influenza vaccine (RIV) in pregnant women is limited, though it is considered acceptable for use 1
• Early vaccination (during July and August) can be considered for women in their third trimester during these months to provide protection for the infant during the first months of life 1

Addressing Safety Concerns

• One observational Vaccine Safety Datalink study during the 2010-2011 and 2011-2012 seasons initially suggested an association between receipt of H1N1pdm09-containing vaccine and risk of spontaneous abortion when the same vaccine had been received the previous season 1
• However, a follow-up study by the same investigators with a larger population and stricter outcome measures did not confirm this association, further supporting the safety of influenza vaccine during pregnancy 1
• Most studies have not noted any association between influenza vaccination and adverse pregnancy outcomes, including spontaneous abortion 1, 3

Clinical Practice Recommendations

• Healthcare providers should strongly recommend and offer influenza vaccination to all pregnant patients 4, 5
• Women offered influenza vaccination by a healthcare provider are significantly more likely to be vaccinated (71%) compared to those not offered (14%) 4
• No special precautions or observation periods are needed when administering influenza vaccines to pregnant women 1, 6
• Vaccination during breastfeeding is also safe for mothers and their infants 1

In summary, the evidence strongly supports that influenza vaccination is safe at any gestational age during pregnancy, with no increased risk of adverse outcomes for either the mother or the developing fetus, while providing significant protection against influenza-related complications.