Is the inactivated influenza vaccine safe for pregnant women at any trimester?

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Inactivated Influenza Vaccine is Safe During Any Trimester of Pregnancy

The inactivated influenza vaccine (IIV) is safe and recommended for pregnant women during any trimester of pregnancy, and should be administered as soon as available during influenza season. 1

Key Recommendations

Vaccine Type and Timing

  • Any licensed, recommended, age-appropriate IIV can be safely administered during any trimester of gestation and postpartum 1
  • The live attenuated influenza vaccine (LAIV) is contraindicated during pregnancy 1
  • Vaccination can occur at any time during pregnancy, before and during influenza season, with no need to delay based on trimester 1

Safety Evidence

First Trimester Safety:

  • A 5-year retrospective cohort study of more than 10,000 women found no association between first-trimester vaccination and 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

Pregnancy Outcomes:

  • Most studies report either a protective effect or no association with preterm birth and small-for-gestational-age infants 1
  • A cohort study from the Vaccines and Medications in Pregnancy Surveillance System (2010-2014 seasons) found no significant association between spontaneous abortion and influenza vaccine exposure in the first trimester or within the first 20 weeks of gestation 1

Important Nuance on Spontaneous Abortion Data

One observational Vaccine Safety Datalink study during 2010-2011 and 2011-2012 seasons noted an association between IIV containing H1N1pdm09 and spontaneous abortion risk when an H1N1pdm09-containing vaccine had also been received the previous season 1. However, a larger follow-up study with stricter outcome measures did not reveal this association and further supported vaccine safety during pregnancy 1.

Clinical Benefits

Maternal Protection

  • Pregnant women are at higher risk for severe illness, hospitalization, and complications from influenza, particularly during the second and third trimesters 1
  • Vaccination reduces risk of respiratory illness and influenza in pregnant and postpartum persons 1

Infant Protection

  • Infants born to vaccinated mothers have up to 72% risk reduction (95% CI, 39%-87%) for laboratory-confirmed influenza hospitalization in the first few months of life 1
  • Protection occurs through transplacental passage of antibodies during pregnancy 1
  • Maternal vaccination protects infants during their first 6 months of life when they are too young to receive influenza vaccine themselves 1

Practical Implementation

Vaccine Administration

  • No special precautions beyond standard vaccination practices are required 1
  • The FDA pregnancy exposure registry is available for healthcare providers to report outcomes: call 1-800-822-2463 or visit sanofipasteurpregnancyregistry.com 2

Breastfeeding

  • Vaccination during breastfeeding is safe for both mothers and infants 1
  • Human milk from mothers vaccinated during the third trimester contains higher levels of influenza-specific immunoglobulin A 1
  • Greater exclusivity of breastfeeding in the first 6 months decreases respiratory illness episodes with fever in infants of vaccinated mothers 1

Common Pitfall to Avoid

Do not delay vaccination due to concerns about first-trimester safety—the evidence strongly supports safety across all trimesters 1. Despite low vaccination rates (only 38.1% during 2023-2024 season) 1, the benefits clearly outweigh any theoretical risks 1.

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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