RSV Immunization Effectiveness and Safety for the 2026-2027 Respiratory Season

Importance: Respiratory syncytial virus (RSV) is a leading cause of acute respiratory tract infection and a contributor to morbidity and mortality. Objective: To synthesize evidence from recent randomized clinical trials and observational studies reporting on the effectiveness and safety of RSV vaccines and monoclonal antibodies and the epidemiology of RSV in the US. Evidence Review: Databases including MEDLINE (PubMed), Embase, Cochrane CENTRAL, and Scopus were searched from August 1, 2025, through June 29, 2026, for studies evaluating the safety and effectiveness of US-licensed RSV vaccines or RSV monoclonal antibody products or describing RSV epidemiology. Data were extracted for older adults (≥60 years), adults, immunocompromised persons, infants, children, and individuals vaccinated during pregnancy. Reviewers assessed risk of bias (RoB) using Cochrane tools for randomized and observational studies. Findings: A total of 75 eligible studies were identified, including 12 randomized clinical trials (RCTs), 33 observational studies with a comparator group, 16 observational studies without a comparator group, and 14 descriptive studies on RSV epidemiology. Among older adults, RSV vaccination was associated with a reduction in RSV-related hospitalization (vaccine effectiveness [VE], 83.3%; 95% CI, 42.9% to 96.9%). Point estimates for RSV VE against hospitalization and laboratory-confirmed RSV illness among older adults were significantly higher during the first season after vaccination compared with 12 to 18 months of follow-up in 1 study, although the difference was not significant when comparing VE after 1 season vs 2 seasons in another study. The VE for maternal vaccination (between 32-36 weeks' gestation) ranged from 51.0% (95% CI, -29.6% to 83.3%) to 70.0% (95% CI, 37.0% to 86.0%) against RSV-related infant hospitalization. Estimates for effectiveness of nirsevimab among infants varied by timing ranged from 63.6% (95% CI, 26.9% to 81.9%) to 93.0% (95% CI, 83.0% to 97.0%) for RSV-related hospitalization within 6 to 12 months. No cases of Guillain-Barré syndrome (GBS) were identified across 3 RCTs; among older adults, 1 self-controlled case series reported a possible increased risk of GBS during the 42 days following vaccination. None of the comparative studies included in this review found an association of RSV vaccination during pregnancy with preterm birth or other adverse pregnancy outcomes. Conclusions and Relevance: RSV immunizations were associated with reduced risk of severe RSV and RSV-related hospitalizations; evidence among older adults suggests that RSV VE may be lower in subsequent seasons. Reported adverse events of special interest (including GBS and preterm birth) were consistent with prior reviews. The results of this updated review are both consistent with previously reported evidence and provide new insight into several aspects of RSV immunizations.