Coadministered Influenza- and Pertussis-Containing Vaccines in Pregnant Women.

Importance: Safety concerns are a barrier to vaccination during pregnancy. Although same-day administration of multiple vaccines may maximize uptake in pregnant women, few studies have focused on the safety of concomitant vaccination during pregnancy. Objective: To assess rates of pregnancy, birth, and neonatal outcomes following concomitant administration of influenza- and pertussis-containing vaccines in pregnant women compared with a matched control group. Design, Setting, and Participants: This population-based cohort study retrospectively analyzed linked data from perinatal and immunization registers and hospitalization data for women with singleton pregnancies in New South Wales, Australia, with estimated last menstrual period between January 1, 2021, and March 12, 2022, and their infants. Concomitant influenza and pertussis vaccination was compared with pertussis vaccination alone after 1:1 matching with replacement on vaccination date, gestation at vaccination, and maternal age. Data were analyzed between April and August 2025. Exposure: Women who received concomitant influenza- and pertussis-containing vaccine administration at 20 weeks' gestation or later were compared with those who received pertussis vaccination alone (control group). Main Outcomes and Measures: Primary outcomes were preterm birth, stillbirth, small for gestational age, and low birth weight. Secondary outcomes were antepartum hemorrhage, postpartum hemorrhage, chorioamnionitis, preeclampsia or eclampsia, prelabor rupture of membranes, and preterm labor. Pregnancy and birth outcomes were assessed using Cox models, and neonatal outcomes were assessed using logistic regression. Results: A total of 13 918 singleton pregnancies (6959 with concomitant vaccination matched to 6959 with pertussis vaccination alone) in women with a mean (SD) maternal age at delivery of 31.7 (4.9) years were analyzed. There were 264 (3.8%) preterm births in the concomitant vaccination group and 302 (4.4%) in the matched control group. Among term live births only (6391 pairs), 565 (8.8%) infants in the concomitant vaccination group and 633 (9.9%) in the control group were small for gestational age and 107 (1.7%) infants in the concomitant vaccination group and 105 (1.6%) in the control group had low birth weight. There were 17 (0.1%) stillbirths in the total matched cohort, precluding further analysis. No difference in the rate of preterm birth (adjusted hazard ratio, 0.83; 95% CI, 0.66-1.05) or the odds of small for gestational age (adjusted odds ratio [OR], 0.87; 95% CI, 0.74-1.04) or low birth weight (adjusted OR, 0.94; 95% CI, 0.66-1.35) between the matched groups was observed. There were no differences in rates between the concomitant vaccination and control groups for the secondary outcomes. Conclusions and Relevance: In this cohort study, no association was found between concomitant influenza- and pertussis-containing vaccine administration during pregnancy and an increased rate of adverse pregnancy, birth, or neonatal outcomes compared with pertussis vaccination alone. These findings may help clinicians more confidently recommend vaccination concomitantly during pregnancy and potentially provide more opportunities to optimize uptake.