Acute viral bronchiolitis before and after implementation of <i>nirsevimab</i> prophylaxis in Italy: a multicentre retrospective cohort study.
retrospective_cohort · Level III
Where this comes from
- Record sourced from PubMed, PMID 42666909.
- Also identified by DOI 10.1016/j.lanepe.2026.101823 and PMC identifier 13524486.
- Licence recorded as CC BY-NC-ND.
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Abstract
Acute viral bronchiolitis is the leading cause of hospitalisation in the first year of life, with Respiratory Syncytial Virus (RSV) accounting for more than 60% of cases. A long-acting monoclonal antibody (<i>nirsevimab</i>) has been introduced for infants entering their first epidemic season. 2024-2025 season was the first with <i>nirsevimab</i> availability in Italy. We assessed its impact on bronchiolitis-related utilisation and clinical and virological characteristics of hospitalised infants. We conducted a multicentre retrospective cohort study including infants <12 months with all-cause bronchiolitis during two seasons: pre-implementation (October 2023-April 2024) and post-implementation (October 2024-April 2025). Data were collected from 30 university hospitals across 15 regions using ICD-10 codes. Outcomes were compared using propensity score matching and multivariate regression analyses. Following implementation, emergency department visits decreased by 48% (5076 vs 2633), pediatric ward admissions by 48% (2734 vs 1473) and pediatric intensive care unit admissions by 61% (334 vs 131). Analyses adjusted for local rollout showed reductions of 82% (RR 0.18), 84% (RR 0.16) and 79% (RR 0.20), respectively. Post-implementation, infants were older (aOR 1.07, 95% CI 1.04-1.10) with lower odds for low- (aOR 0.67, 95% CI 0.55-0.82) and high-flow (aOR 0.8; 95% CI 0.65-0.99) oxygen-therapy. RSV remained predominant (934/1473, 63%), while non-RSV infections increased (334/2734, 12% vs 305/1473, 21%). Most infants had not received prophylaxis; 372 (25%) hospitalised despite <i>nirsevimab</i> were younger (5.2 ± 3.5 vs 2.8 ± 1.9, p < 0.001) and had more comorbidities (11%, 82/745 vs 22%, 37/168, p < 0.001). In Italy, <i>nirsevimab</i> was associated with reduced all-cause bronchiolitis-related utilisation and milder disease. Underlying conditions remained a determinant for severe outcomes despite prophylaxis. No funding was received for this study.