A new University of Iowa research study examining possible associations between maternal influenza vaccination and a host of major structural birth defects reaffirms the safety of the vaccination during early pregnancy.

The study, led by Paul Romitti, University of Iowa Distinguished Chair, professor of epidemiology, and director of the Iowa Registry for Congenital and Inherited Disorders, analyzed data from the U.S. Birth Defects Study to Evaluate Pregnancy exposureS (BD-STEPS) which is funded by the U.S. Centers for Disease Control and Prevention. The research, published in the journal Vaccine, focused on deliveries in the years 2014-2019 to examine early pregnancy influenza vaccine uptake and risk prior to the COVID-19 pandemic.

The investigators assessed mothers’ influenza vaccination status during early pregnancy for several birth defects, including central nervous system, craniofacial, ear, gastrointestinal, heart, limb, and musculoskeletal defects. The study sample included over 4200 mothers.

The findings showed no statistically significant positive associations between influenza vaccination and the selected birth defects, according to Romitti.

“These results reinforce the safety of influenza vaccination during pregnancy, which is a key strategy for reducing health threats that influenza infections can pose to pregnant women and their newborns,” Romitti says.

The authors acknowledged that concern about potential risk to fetal safety is a barrier to maternal vaccination, noting that despite global and U.S. health recommendations for influenza vaccination during pregnancy, only around 60% of pregnant women typically receive the seasonal vaccine.

“To maintain public confidence in vaccine safety and optimize maternal and fetal health outcomes, it is important to continue to evaluate the safety of maternal vaccinations using well-characterized, population-based datasets encompassing children with and without major birth defects,” according to the report.

Romitti also noted that components of the influenza vaccine may change from one year to another, requiring ongoing evaluation of the safety of seasonal vaccinations.

The current study extends the research group’s previous work that examined risk for over 30 major structural birth defects among births 2006-2011, which also supported the safety of maternal influenza vaccination.

‘Influenza vaccination during early pregnancy and risk of major birth defects, US Birth Defects Study To Evaluate Pregnancy exposureS, 2014–2019’ by Veronica Malange, Tasnim Mohaissen, et al. https://doi.org/10.1016/j.vaccine.2025.127297, as published in Vaccine, Volume 59 (20 June 2025), by Elsevier. 

Vaccine is the pre-eminent journal in the field of vaccinology. It is the official journal of The Japanese Society for Vaccinology and is published by Elsevier. Copies of this paper are available to credentialed journalists upon request, please contact the Elsevier Newsroom at newsroom@elsevier.com‘