Maternal RSV Vaccine Cuts Infant Hospitalization Risk by Nearly 70% in Real-World Study
New real-world data confirm that RSV vaccination during pregnancy protects newborns from severe respiratory illness, mirroring clinical trial results.
Summary
A retrospective study published in JAMA Network Open confirms that the maternal RSV vaccine (Abrysvo) is highly effective at preventing infant hospitalizations in real-world settings. Among infants 90 days old or younger, the vaccine reduced RSV-related hospitalization risk by 67.6%. For the most vulnerable newborns — those 30 days old or younger — effectiveness reached 74.2%. These findings span two RSV seasons and closely match the original phase III MATISSE clinical trial results, giving physicians and parents strong confidence that vaccination during the third trimester of pregnancy meaningfully protects infants during their most vulnerable early weeks of life.
Detailed Summary
Respiratory syncytial virus (RSV) is a leading cause of infant hospitalization, particularly dangerous in the first months of life. Researchers have now confirmed that vaccinating pregnant mothers against RSV provides robust real-world protection for their newborns, adding critical evidence beyond the original clinical trial.
The CASSATT study, a retrospective test-negative case-control analysis using electronic health records from the University of Pittsburgh Medical Center, evaluated mothers vaccinated between gestational weeks 32 and 36. It covered two consecutive RSV seasons from late 2023 through early 2025, including infants born at 32 weeks gestation or later.
Key findings showed vaccine effectiveness of 67.6% against RSV-associated acute respiratory illness hospitalization in infants up to 90 days old, and 74.2% in those up to 30 days old. Protection against lower respiratory tract disease hospitalization reached 69%. These numbers closely mirror the phase III MATISSE trial, where efficacy was 81.8% within 90 days of birth for severe cases.
The consistency between trial and real-world data is particularly meaningful because real-world populations include higher-risk infants and more variable conditions than controlled trials. Researchers emphasized that protection applied broadly across different infant demographics and risk profiles.
For parents and clinicians, this study strengthens the case for maternal RSV vaccination during pregnancy as a cornerstone preventive strategy. It also exists alongside infant-directed options like monoclonal antibodies nirsevimab (Beyfortus) and clesrovimab (Enflonsia), suggesting that personalized protection plans are now feasible. Caveats include the single health system setting, limiting generalizability, and the retrospective design, which cannot fully eliminate confounding. Larger multicenter studies would further solidify these conclusions.
Key Findings
- Maternal RSV vaccine showed 67.6% effectiveness against infant RSV hospitalization in infants up to 90 days old.
- Effectiveness rose to 74.2% in newborns 30 days or younger, protecting the most vulnerable infants.
- Real-world results closely matched the phase III MATISSE clinical trial efficacy data across two RSV seasons.
- Protection extended to lower respiratory tract disease hospitalization with 69% vaccine effectiveness.
- Parents now have multiple RSV protection options including maternal vaccine and infant monoclonal antibodies.
Methodology
This is a research summary reporting findings from a peer-reviewed retrospective test-negative case-control study published in JAMA Network Open, a credible open-access journal. The CASSATT study used electronic health record data from a single major academic health system across two RSV seasons. Evidence quality is moderate-high given real-world design but limited by single-center scope.
Study Limitations
The study was conducted within a single health system, which may limit generalizability to broader or more diverse populations. Retrospective case-control design cannot fully exclude confounding variables such as socioeconomic factors or healthcare-seeking behavior. Primary source review in JAMA Network Open is recommended for full methodology and statistical detail.
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