A recent real-world study in the United States found that maternal vaccination with the RSV prefusion F vaccine was associated with a lower risk of hospitalization for respiratory syncytial virus (RSV) disease among infants during their first three months of life, according to a June 16 report.
The study, published in JAMA Network Open, examined outcomes for 274 hospitalized infants aged 90 days or younger who were tested for RSV over two RSV seasons from 2023 to 2025. The researchers compared maternal vaccination rates between infants who tested positive for RSV and those who did not. They estimated vaccine effectiveness against hospitalization due to acute respiratory illness (ARI) and lower respiratory tract disease (LRTD) related to RSV from birth through the first 90 days of life.
Results showed that about 30% of all infants in the cohort were born to mothers who received the prefusion F vaccine. Among control subjects—infants without RSV—37% had vaccinated mothers, compared with only 13% among cases—infants with confirmed RSV infection. The estimated effectiveness of maternal vaccination within the recommended gestational window and at least two weeks before delivery was reported as 68% against infant hospitalization due to ARI caused by RSV, and 69% against LRTD-related hospitalizations during the same period. In the first month after birth, estimated vaccine effectiveness rose to 74%. These findings are consistent with results from clinical trials that led to approval of this vaccine.
The authors noted that most cases occurred among babies born between October and December, and these infants were more likely than controls to be preterm, male, Black, have siblings, or live in areas with higher deprivation levels. A higher proportion of cases required intensive care unit admission or oxygen support compared with controls.
The research used data from a single health system in western Pennsylvania following introduction of the bivalent prefusion F vaccine approved for use during pregnancy in the United States since 2023. Limitations include its observational design—which does not allow causal inference—a small sample size resulting in wide confidence intervals, especially for subgroup analyses, and restriction to one healthcare system.
Pfizer supported this study through collaboration with the University of Pittsburgh; several authors disclosed Pfizer employment or grant support. According to disclosures included by the authors, "Pfizer reviewed and approved the manuscript but had no role in data collection, management, analysis, or decision to submit it." The findings suggest that maternal immunization may be an effective strategy for preventing severe early-life RSV disease.
