Maternal RSV Vaccine Linked to Lower Risk of Infant Hospitalization

Maternal respiratory syncytial virus (RSV) vaccination during pregnancy was effective at preventing infants from being hospitalized with RSV-associated acute respiratory illness (ARI) in a real-world setting, according to a retrospective case-control study.

Among infants ages 90 days or younger, the estimated vaccine effectiveness with maternal RSV prefusion F (RSVpreF; Abrysvo) was 67.6% (95% CI 33.2-85.4) against RSV-associated ARI hospitalization and 69% (95% CI 25.5-88.0) against RSV-associated lower respiratory tract disease hospitalization, reported Anne-Marie Rick, MD, MPH, PhD, of the University of Pittsburgh School of Medicine, and colleagues in JAMA Network Open.

Among infants ages 30 days or younger, estimated vaccine effectiveness against RSV-associated ARI hospitalization was 74.2% (95% CI 25.4-93.0).

Those estimates spanned the first two RSV seasons that the vaccine was available, and the numbers mirror the efficacy rates seen in the phase III MATISSE trial, which showed that the RSVpreF vaccine administered in the third trimester had a vaccine efficacy of 81.8% against severe RSV cases in infants within 90 days of birth (99.5% CI 40.6-96.3) and 69.4% within 180 days of birth (97.58% CI 44.3-84.1).

“It’s very reassuring that we have multiple RSV seasons and very much a real-world situation with higher-risk cases, and we’re finding almost identical findings to the clinical trial,” Rick told MedPage Today. “This is real protection, and it really applies to all comers, in terms of what we can expect for protection of children.”

The findings are important for parents making decisions about how to best protect their children, Rick added. “Knowing that the RSV vaccine can be given in pregnancy and really translates into real protection for their infants when they’re most vulnerable is critical to informing those decisions for parents.”

Having the RSV vaccine for pregnant mothers and the immunization monoclonal antibodies nirsevimab (Beyfortus) and clesrovimab (Enflonsia) for infants gives parents protective options, Rick explained. “Data like these will help start informing how we individualize those decisions for specific families.”

The ongoing retrospective, test-negative, case-control CASSATT study is evaluating maternal RSVpreF vaccination effectiveness against hospitalization for RSV-associated ARI and lower respiratory tract disease using electronic health record data from infants born and later admitted at hospitals in the University of Pittsburgh Medical Center health system.

The current analysis included infants born at gestational age 32 weeks or older between October 2023 and April 2024, or September 2024 through April 2025. Mothers had reached the RSVpreF vaccination window of gestational age 32 weeks 0-7 days to 36 weeks 6-7 days during local RSV vaccination seasons. Infants who received one of the RSV monoclonal antibodies or were born to a mother who received an RSV vaccine other than RSVpreF were excluded.

Among the 274 included infants, mean gestational age at birth was 38.3 weeks, mean age at hospital admission was 29.5 days, 52.2% were boys, 62.4% were white, 13.5% were Black, and 3.6% were Hispanic. About 13% of infants had a pre-existing complex medical condition at hospital admission. Among infants with RSV, 21.7% were preterm, 56.6% were male, 83.1% had one or more siblings, and 30.1% were in the highest area deprivation index quartile.

Thirty percent of infants were born to a mother who received the RSVpreF vaccine, including 13.3% of infants with RSV and 37.2% of those without RSV. Nearly two-thirds of infants with RSV (60.2%) were admitted to the hospital in December and January compared with 30.4% of those without RSV.

Effectiveness increased with greater time between vaccination and delivery. While the rate was 64.7% with maternal vaccination between 14 days and 27 days from delivery, it rose to 67.5% when RSVpreF was given at least 28 days before delivery.

The study’s relatively small sample size led to wider 95% confidence intervals, Rick and team noted, but “the consistency of point estimates across randomized and clinical studies supports a similar magnitude of protection during early infancy.”

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