Efficacy and safety of a single dose of nirsevimab against respiratory syncytial virus infection in infants: a meta-analysis and time-to-event analysis

Respiratory syncytial virus (RSV) is one of the causes of lower respiratory tract infections (LRTIs) and related hospitalizations in neonates and infants. Clinical trials have shown that a single dose of nirsevimab can prevent this infection and its related complications. We systematically searched PubMed, Embase, Web of Science (WOS), Scopus, and Cochrane Central on 25 November 2024 and updated on 18 April 2025, without automated filters or language restrictions. Studies reported the outcomes after nirsevimab in infants were retrieved. A random effects model was applied for analysis. A total of 425,362 infants were pooled from 26 studies (6 randomized controlled trials and 20 observational cohorts studies). The immunization with nirsevimab reduced the incidence of RSV-LRTIs by 63% (risk ratio [RR]: 0.37; 95% CI [0.29; 0.47], p-value < 0.001, I² = 91.77%), hospitalization by 73% (RR: 0.27; 95% CI [0.20; 0.37], p-value < 0.001, I² = 97.46%). Nirsevimab also reduced the incidence of all-cause LRTIs and hospitalization, bronchiolitis, ICU admission, emergency unit visits, and all-cause mortality. The high heterogeneity was raised from pooling the real-world data across different clinical settings such as different geographical locations. There was no statistical significance regarding safety outcomes; serious, GIT adverse events, adverse events of special interest, and adverse events > grade 3 between the two groups. The time to event analysis showed that nirsevimab significantly reduced the RSV-LRTIs (Hazard Ratio (HR): 0.25; 95% CI [0.16; 0.37]) and hospitalization (HR: 0.14; 95% CI [0.08; 0.25]). The immunization with a single dose of nirsevimab significantly reduced the RSV-LRTIs and hospitalization in infants who were at risk for RSV infection without any identified safety concerns. The long-term safety concerns are still unclear across the current studies.