Early real-world evidence suggests that maternal vaccination with a bivalent prefusion F subunit–based RSV vaccine (RSVpreF; Abrysvo, Pfizer) during late pregnancy is not associated with increased risk for several key adverse pregnancy outcomes, according to a new study published in JAMA (2026;335;[5]:456-459).
The findings provide early reassurance regarding the safety of the vaccine as national recommendations evolve and uptake increases.
No Increased Preterm Birth, Hypertension With Vaccination
The observational cohort study evaluated outcomes among nearly 7,000 vaccinated pregnancies, focusing on vaccinations administered during the FDA-approved gestational window of 32 through 36 weeks. Investigators assessed risks for outcomes including preterm birth and hypertensive disorders of pregnancy.
In adjusted analyses, preterm birth occurred in 4.2% of vaccinated pregnancies and 5.5% of unvaccinated pregnancies, with no statistically significant increase in risk associated with RSVpreF vaccination. Risks of hypertensive disorders of pregnancy were similar between groups, and no statistically significant differences were observed for other outcomes assessed, including prelabor rupture of membranes (PROM) and preterm PROM.
“Given the understandable questions many families and clinicians have about new vaccines in pregnancy, these early results are encouraging,” said lead author Ashley I. Michnick, PharmD, PhD, a research associate at the Harvard Medical School Department of Population Medicine, in Boston. “In real-world data from thousands of pregnancies, we saw no sign of increased risks of the outcomes we evaluated, including preterm birth and hypertensive disorders of pregnancy.”
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Building on Previous Positive Data
Dr. Michnick noted that the study addresses an important gap left by earlier studies.
“These findings are crucial because they differ from available clinical trial data in an important way: we investigated vaccinations given during the U.S. FDA-approved window of 32 through 36 weeks’ gestation, instead of beginning the window at 24 weeks as was done in this vaccine’s large randomized controlled trial before approval,” she said.
According to Dr. Michnick, the study builds on a series of rapid cycle safety analyses conducted shortly after vaccine approval and precedes additional planned evaluations.
“This study is just one part of a comprehensive safety surveillance plan for this vaccine’s use in pregnancy,” she said. “It was preceded by a series of five back-to-back safety analyses and will be followed by two more interim reports before a final cohort study in 2029.”
The authors noted that the interim cohort was drawn primarily from a commercially insured population that was largely white and non-Hispanic, which may limit generalizability.
“Our future studies including more generalizable populations—especially pregnancies covered by public insurance such as Medicaid—will be important,” Dr. Michnick said. “Larger and more generalizable populations moving forward may reveal different effect estimates.”
Dr. Michnick reported no relevant financial disclosures.