Association of Respiratory Syncytial Virus Vaccination During Pregnancy With Adverse Obstetric and Neonatal Outcomes

To assess adverse pregnancy and birth outcomes after bivalent prefusion F subunit-based respiratory syncytial virus vaccine (RSVpreF) vaccination during the first season of availability.

This was a target trial emulation study including eight health systems across eight states (California, Oregon, Washington, Colorado, Maryland, Virginia, Minnesota, and Wisconsin) and Washington, DC, in the Vaccine Safety Datalink (VSD). We included pregnant patients aged 16-49 years who had enrolled at a VSD site between September 22, 2023, and February 29, 2024. Exposure was defined as receipt of RSVpreF vaccination between 32 and less than 37 weeks of gestation. Outcomes included preterm birth (PTB), stillbirth, small-for-gestational-age (SGA) birth weight, and hypertensive disorders of pregnancy (HDP) assessed with electronic health record data. Stillbirth cases were confirmed through chart review. Pregnant patients exposed to RSVpreF vaccines were matched 1:1 to unexposed pregnant patients at the gestational week of vaccination by propensity to be vaccinated and VSD site. Unexposed pregnant patients were assigned an index date equivalent to the gestational day of vaccination for their vaccinated match. If the unvaccinated match was subsequently vaccinated, the pair was censored. We report adverse event risks and adjusted risk ratios (aRRs) with corresponding 95% CIs adjusted for nulliparity using a log binomial model with robust variance.

We identified 13,966 pregnant patients who received the RSVpreF vaccine. A higher percentage of nulliparous patients were in the vaccinated group (46.4%) compared with the unvaccinated group (38.7%). Comparing RSVpreF vaccinated pregnant patients and their unvaccinated matches, rates of PTB (4.0% vs 4.5%, respectively; aRR 0.90, 95% CI, 0.80-1.00), stillbirth (0.79/1,000 and 0.72/1,000; aRR 0.99, 95% CI, 0.41-2.36), and SGA birth weight (6.8% and 6.5%; aRR 1.02, 95% CI, 0.92-1.12) did not significantly differ. The rate of any HDP among RSVpreF vaccinated patients was 17.3% vs 15.0% among their unvaccinated matches (aRR 1.13, 95% CI, 1.07-1.19).

Initial prenatal RSVpreF safety surveillance shows a largely favorable safety profile. Although we identified a small but statistically significant increased risk for HDP after RSVpreF vaccination, there was no increased risk for PTB, SGA birth weight, or stillbirth.