Association of Influenza Vaccination During Pregnancy with Health Outcomes in Mothers and Children: A Population-Based Cohort Study

Immunization rates of maternal influenza vaccination during pregnancy remain suboptimal, with concerns about potential harm to the mothers and their offspring. We conducted a population-based cohort study, using mother-child linked database in Korea: (a) maternal cohort between December 2019, and March 2022; (b) neonatal cohort between September 2020, and June 2021. Exposure was defined as influenza vaccination during pregnancy. Study outcomes included gestational outcomes, vaccine-related adverse events, and other health outcomes in mothers and childbirth and immune-related health outcomes in children. After 1-to-1 propensity score matching using diverse potential confounders, effect estimates with 95% confidence intervals were estimated using the log-binomial model for cumulative outcomes and the Cox proportional model for time-to-event outcomes. After 1-to-1 propensity score matching, we identified 174,008 and 53,344 pairs for the maternal and neonatal cohorts, respectively. In the maternal cohort, influenza vaccination during pregnancy was not associated with preeclampsia, antenatal bleeding, and various adverse outcomes, including neurological, vascular, blood, and lymphatic system disorders, except for marginally elevated risks of gestational diabetes mellitus (effect estimate 1.06, 95% confidence interval 1.05 to 1.08) and postpartum hemorrhage (1.05, 1.01 to 1.08). In the neonatal cohort, maternal influenza vaccination did not increase risks of childbirth (e.g., preterm/low birth weight, congenital malformations, mortality) and immune-related outcomes, except for a slightly increased risk of lower respiratory tract infection (1.06, 1.007 to 1.12). In this population-based cohort study, influenza vaccination during pregnancy was not associated with an increased risk of a range of adverse outcomes in mothers and their offspring.