First-Season Nirsevimab Linked to Fewer Second-Season LRTI Admissions

Nirsevimab administration during infants’ first respiratory syncytial virus (RSV) season was associated with fewer hospitalizations for lower respiratory tract infection (LRTI) during their second respiratory season, according to a case-control study published online July 28 in Pediatrics.

The community-based study was conducted at 9 tertiary pediatric hospitals in Andalusia, southern Spain. It included infants born from April 1, 2023, through March 31, 2024. Cases were infants hospitalized for LRTI during the 2024 to 2025 season; for each case, investigators selected 4 community controls matched by birthdate and province.

Exposure was nirsevimab administration during the 2023 to 2024 RSV season, and the main outcome was LRTI hospitalization during the following season. Investigators used inverse probability weighting and doubly robust augmented inverse probability weighting models to estimate the average treatment effect as an absolute risk reduction.

The analysis included 1375 infants: 275 cases and 1100 controls. In the augmented model, first-season nirsevimab administration was associated with a 17.0% absolute risk reduction in second-season LRTI hospitalization (95% CI, 3.2%-30.8%). Stronger associations were reported among RSV-positive cases (25.4%; 95% CI, 4.9%-45.8%) and infants with a history of inhaler use (27.7%; 95% CI, 6.4%-48.9%).

A negative-control analysis using rotavirus vaccination found no association, which the investigators said provided no evidence of relevant residual confounding related to health-seeking behavior. The authors concluded that nirsevimab administration was associated with reduced second-season LRTI hospitalization suggesting meaningful benefits beyond the season of administration and said the findings may have implications for future cost-effectiveness evaluations.

Sources: Moreno-Pérez D, Catalán-Fernández E, Croche-Santander B, et al. Nirsevimab and hospitalization for lower respiratory tract infection during the second season. Pediatrics. Published online July 28, 2026. doi:10.1542/peds.2025-075562