Results from a large population-based study found that receiving influenza and pertussis vaccines on the same day during pregnancy does not increase the risk of adverse maternal, birth, or neonatal outcomes compared with pertussis vaccination alone.
Safety concerns remain one of the most persistent barriers to vaccination during pregnancy, particularly when multiple vaccines are recommended within a relatively short time frame. As maternal immunization strategies expand to include protection against influenza, pertussis, COVID-19, and respiratory syncytial virus, questions about the safety of administering more than 1 vaccine at the same visit have become increasingly relevant.
A large population-based cohort study conducted in Australia offers important reassurance. Researchers analyzed data from 13,918 singleton pregnancies, comparing outcomes among women who received concomitant influenza and pertussis vaccines at 20 weeks’ gestation or later with those who received the pertussis vaccine alone. The groups were carefully matched based on vaccination timing, gestational age, and maternal age to ensure a robust comparison.
The findings showed no evidence of increased risk associated with concomitant vaccination. Preterm birth occurred in 3.8% of women who received both vaccines simultaneously compared with 4.4% in the control group. After statistical adjustment, this difference was not significant, indicating that receiving both vaccines on the same day does not elevate preterm birth risk.
The study also examined a range of neonatal outcomes among term births. Rates of children born small for gestational age were slightly lower in the concomitant vaccination group (8.8%) compared with the control group (9.9%), whereas rates of low birth weight were nearly identical (1.7% vs 1.6%). Again, none of these differences reached statistical significance.
Concomitant influenza and pertussis vaccination during pregnancy was not associated with higher rates of preterm birth, low birth weight, or newborns small for gestational age.
Maternal complications and neonatal outcomes were similar between women receiving simultaneous vaccines and those receiving pertussis vaccine alone.
The findings support same-day vaccination as a practical strategy to improve coverage during pregnancy without compromising safety.
Stillbirths were rare, with only 17 cases observed across the entire matched cohort, limiting the ability to draw meaningful comparisons. However, the low number itself reinforces the overall safety profile observed in both groups.
In addition to primary outcomes, researchers assessed several maternal complications, including preeclampsia, antepartum and postpartum hemorrhage, chorioamnionitis, prelabor rupture of membranes, and preterm labor. No differences were observed between the concomitant vaccination group and the control group for any of these outcomes.
To strengthen confidence in the findings, the analysis adjusted for a range of potential confounders, including socioeconomic status, smoking during pregnancy, and COVID-19 vaccination status. Sensitivity analyses—such as alternative matching approaches and exclusion of certain subgroups—yielded consistent results, underscoring the robustness of the conclusions.
