Is the flu vaccine safe for pregnant women?

Flu Vaccine Safety During Pregnancy

The inactivated influenza vaccine is safe and strongly recommended for pregnant women during any trimester of pregnancy, with both the CDC and WHO prioritizing pregnant women for vaccination to reduce serious maternal and fetal complications. 1, 2

Current Guideline Recommendations

Both major health organizations recommend universal influenza vaccination during pregnancy:

• The CDC recommends one dose of seasonal inactivated influenza vaccine during any trimester of pregnancy 1, 2
• The WHO advises that pregnant women should be prioritized to receive the seasonal influenza vaccine year-round, given their increased vulnerability 1
• The American College of Obstetricians and Gynecologists, American Academy of Pediatrics, and American Academy of Family Physicians all consistently endorse vaccination during any trimester 2, 3

Safety Evidence Across All Trimesters

The safety profile of inactivated influenza vaccine during pregnancy is well-established:

• No increased risk of major congenital malformations was found in a 5-year retrospective cohort study of over 10,000 women who received first-trimester vaccination 2, 4
• A systematic review and meta-analysis of 15 studies demonstrated no association between congenital defects and influenza vaccination in any trimester, including the first 2, 4
• Studies of more than 2,000 pregnant women have shown no adverse fetal effects associated with influenza vaccine 1
• Inactivated vaccines are generally considered safe for use during pregnancy 1, 5

Critical Distinction: Vaccine Type Matters

Only inactivated influenza vaccine (IIV) is safe during pregnancy:

• Inactivated influenza vaccine (trivalent or quadrivalent) is recommended and safe for administration during pregnancy 1, 2
• Live attenuated influenza vaccine (LAIV, nasal spray) is contraindicated during pregnancy due to theoretical risk of placental transmission to the fetus 1, 2, 4
• Recombinant influenza vaccine (RIV) has limited experience in pregnancy but is considered acceptable 2

Why Vaccination Is Critical: Maternal and Fetal Risks

Pregnant women face substantially elevated risks from influenza infection:

• Pregnant women are 7.2% more likely to be hospitalized than non-pregnant women and have disproportionately high mortality risk 1
• The relative risk for hospitalization increases from 1.4 at weeks 14-20 of gestation to 4.7 at weeks 37-42 compared to postpartum women 1, 4
• Women in their third trimester are hospitalized at rates (250 per 100,000) comparable to non-pregnant women with high-risk medical conditions 1
• Influenza infection during pregnancy increases risk of late pregnancy loss (adjusted HR 10.7), reduced birthweight, preterm delivery, and stillbirth 1, 4

Maternal and Infant Benefits of Vaccination

Vaccination protects both mother and infant:

• Prevents 1-2 hospitalizations for every 1,000 pregnant women vaccinated 1
• Infants born to vaccinated mothers have up to 72% risk reduction for laboratory-confirmed influenza hospitalization in the first months of life 2, 4
• Provides passive immunity through transplacental antibody transfer, protecting infants during the first 6 months when they cannot receive their own vaccination 2, 4, 3
• Maternal immunization prevents laboratory-confirmed influenza disease in both mothers and infants during the first 2-6 months of life 2

Addressing Timing Concerns

While any trimester is safe, some nuances exist:

• Current guidelines support vaccination during any trimester, including the first 2, 6
• Some experts historically preferred second-trimester administration to avoid coincidental association with spontaneous abortion, which is common in the first trimester 1
• However, no causal relationship exists between first-trimester vaccination and spontaneous abortion 2
• One observational study initially suggested an association with H1N1pdm09-containing vaccine and spontaneous abortion when the same vaccine was received the previous season, but follow-up studies did not confirm this association 2

Clinical Implementation

No special precautions are needed:

• No special observation periods or precautions are required when administering influenza vaccine to pregnant women 2
• Vaccination is also safe during breastfeeding for both mothers and infants 2, 4
• Any licensed, recommended, age-appropriate inactivated influenza vaccine (IIV3, IIV4, or RIV) may be used 2, 4

Common Pitfall to Avoid

The most critical error is delaying or withholding vaccination due to unfounded safety concerns. Given that pregnant women face substantially higher morbidity and mortality from influenza infection itself, and given the robust safety data spanning thousands of pregnant women across multiple studies, withholding the inactivated influenza vaccine represents a greater risk than administering it 1, 2, 6. The only absolute contraindication is the live attenuated nasal vaccine 1, 2, 4.