Influenza Vaccine Administration in Third Trimester
Yes, the influenza vaccine should absolutely be administered during the third trimester of pregnancy—in fact, vaccination during any trimester is strongly recommended and safe. 1
Primary Recommendation
Both ACIP and the American College of Obstetricians and Gynecologists recommend that all pregnant persons receive influenza vaccine during any trimester of pregnancy, including the third trimester. 1 The vaccine can be administered at any time during pregnancy, before and during the influenza season. 1
Specific Advantages of Third Trimester Vaccination
Early vaccination during July and August should be considered for persons in their third trimester because this provides protection for the infant during the first months of life when they are too young to be vaccinated. 1
Transplacental antibody transfer is most efficient when vaccination occurs in the third trimester, maximizing passive immunity for the newborn. 2
Infants born to vaccinated mothers have up to a 72% risk reduction for laboratory-confirmed influenza hospitalization in the first few months of life. 2, 3
Clinical Rationale for Third Trimester Vaccination
Pregnant women face substantially elevated risks during the third trimester specifically:
The relative risk for hospitalization increases dramatically from 1.4 during weeks 14-20 of gestation to 4.7 during weeks 37-42. 1, 2
Women in their third trimester are hospitalized at rates comparable to non-pregnant women with high-risk medical conditions. 1
Pregnant and postpartum persons are at higher risk for severe illness and complications from influenza, particularly during the second and third trimesters. 1
Vaccine Types Appropriate for Third Trimester
Inactivated influenza vaccine (IIV3) or recombinant influenza vaccine (RIV3) can be used safely. 1
Any licensed, recommended, age-appropriate inactivated influenza vaccine may be administered. 2, 4
Live attenuated influenza vaccine (LAIV3) is contraindicated during pregnancy but can be used postpartum. 1, 2
Safety Profile
The safety data for third trimester vaccination is robust:
Studies of influenza vaccination in more than 2,000 pregnant women have demonstrated no adverse fetal effects. 1
Seasonal inactivated influenza vaccines are well tolerated and immunogenic in pregnant women during the second and third trimester. 5
Multiple prospective studies confirm that vaccines administered in the third trimester are safe with no vaccine-associated serious adverse events. 5, 6
Most studies have not noted any association between influenza vaccination and adverse pregnancy outcomes. 1
Practical Implementation
Vaccination should occur as soon as vaccine becomes available, ideally by the end of October, regardless of trimester. 2, 4 However, vaccination throughout the influenza season is encouraged. 4
For women in their third trimester during July-August when vaccine first becomes available, do not delay vaccination—early administration maximizes infant protection through transplacental antibody transfer. 1
Common Pitfall to Avoid
Do not postpone third trimester vaccination due to concerns about timing relative to delivery. The antibody transfer process is time-dependent, and immunization should ideally occur at least 6 weeks prior to delivery for optimal transplacental antibody transfer. 7 However, vaccination at any point in the third trimester provides benefit and should not be delayed. 1