Background: 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 (nirsevimab) has been introduced for infants entering their first epidemic season. 2024–2025 season was the first with nirsevimab availability in Italy. We assessed its impact on bronchiolitis-related utilisation and clinical and virological characteristics of hospitalised infants. Methods: 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. Findings: 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 nirsevimab 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). Interpretation: In Italy, nirsevimab was associated with reduced all-cause bronchiolitis-related utilisation and milder disease. Underlying conditions remained a determinant for severe outcomes despite prophylaxis. Funding: No funding was received for this study.
Acute viral bronchiolitis before and after implementation of nirsevimab prophylaxis in Italy: a multicentre retrospective cohort study
Coralluzzo, Francesca;Mandato, Claudia;
2026
Abstract
Background: 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 (nirsevimab) has been introduced for infants entering their first epidemic season. 2024–2025 season was the first with nirsevimab availability in Italy. We assessed its impact on bronchiolitis-related utilisation and clinical and virological characteristics of hospitalised infants. Methods: 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. Findings: 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 nirsevimab 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). Interpretation: In Italy, nirsevimab was associated with reduced all-cause bronchiolitis-related utilisation and milder disease. Underlying conditions remained a determinant for severe outcomes despite prophylaxis. Funding: No funding was received for this study.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
