Nonadjuvanted Bivalent Respiratory Syncytial Virus Vaccination and Perinatal Outcomes.

Importance: A nonadjuvanted bivalent respiratory syncytial virus (RSV) prefusion F (RSVpreF [Pfizer]) protein subunit vaccine was newly approved and recommended for pregnant individuals at 32 0/7 to 36 6/7 weeks' gestation during the 2023 to 2024 RSV season; however, clinical vaccine data are lacking. Objective: To evaluate the association between prenatal RSV vaccination status and perinatal outcomes among patients who delivered during the vaccination season. Design, Setting, and Participants: This retrospective observational cohort study was conducted at 2 New York City hospitals within 1 health care system among patients who gave birth to singleton gestations at 32 weeks' gestation or later from September 22, 2023, to January 31, 2024. Exposure: Prenatal RSV vaccination with the RSVpreF vaccine captured from the health system's electronic health records. Main Outcome and Measures: The primary outcome is preterm birth (PTB), defined as less than 37 weeks' gestation. Secondary outcomes included hypertensive disorders of pregnancy (HDP), stillbirth, small-for-gestational age birth weight, neonatal intensive care unit (NICU) admission, neonatal respiratory distress with NICU admission, neonatal jaundice or hyperbilirubinemia, neonatal hypoglycemia, and neonatal sepsis. Logistic regression models were used to estimate odds ratios (ORs), and multivariable logistic regression models and time-dependent covariate Cox regression models were performed. Results: Of 2973 pregnant individuals (median [IQR] age, 34.9 [32.4-37.7] years), 1026 (34.5%) received prenatal RSVpreF vaccination. Fifteen patients inappropriately received the vaccine at 37 weeks' gestation or later and were included in the nonvaccinated group. During the study period, 60 patients who had evidence of prenatal vaccination (5.9%) experienced PTB vs 131 of those who did not (6.7%). Prenatal vaccination was not associated with an increased risk for PTB after adjusting for potential confounders (adjusted OR, 0.87; 95% CI, 0.62-1.20) and addressing immortal time bias (hazard ratio [HR], 0.93; 95% CI, 0.64-1.34). There were no significant differences in pregnancy and neonatal outcomes based on vaccination status in the logistic regression models, but an increased risk of HDP in the time-dependent model was seen (HR, 1.43; 95% CI, 1.16-1.77). Conclusions and Relevance: In this cohort study of pregnant individuals who delivered at 32 weeks' gestation or later, the RSVpreF vaccine was not associated with an increased risk of PTB and perinatal outcomes. These data support the safety of prenatal RSVpreF vaccination, but further investigation into the risk of HDP is warranted.