JAMA Netw Open

Nirsevimab protects against RSV bronchiolitis across two seasons

November 4, 2025

Study details: This multicenter, test-negative case-control study in five French pediatric emergency departments evaluated nirsevimab’s effectiveness during the first two seasons of national implementation (Oct 2023–Feb 2024 and Oct 2024–Jan 2025). The study included 636 infants (<1 year) presenting with first-episode bronchiolitis and tested for RSV. Effectiveness was estimated using multivariable logistic regression adjusted for demographic and clinical factors.

Results:

• RSV accounted for ~71% of bronchiolitis cases in both seasons. Nirsevimab coverage reached 25.5% overall.
• Effectiveness against RSV-positive bronchiolitis was 83.2% in the first season and 89.3% in the second, with no significant difference (P = 0.97).
• Protection remained strong despite RSV-B predominance and reports of resistant mutations.

Clinical impact: These findings support continued use of nirsevimab for RSV prophylaxis in infants, even amid circulating RSV-B variants. The data reinforce its role in reducing emergency visits and hospitalizations, particularly during seasonal peaks, and highlight the need for ongoing surveillance of viral resistance.

Source:

Lenglart L, et al. (2025, October 1). JAMA Netw Open. Nirsevimab Treatment of RSV Bronchiolitis in Pediatric Emergency Departments. https://pubmed.ncbi.nlm.nih.gov/41165704/