RSV bronchiolitis admissions in infants immunized with nirsevimab: a multicenter observational study.

Authors

David Andina Martínez, Esther Fernández Mozo, Nuria Clerigue Arrieta, Jana Izquierdo Frechilla, Amaia Cámara Otegui, Laura Baños López, Gemma Claret Teruel, Manuel Gijón Mediavilla, Clara Ferrero García-Loygorri, Victoria Sánchez Tatay, Silvia Escalada Pellitero, Verónica Gimeno-Hernández Garza, Juan Ventura Pernia Sanchez, Jose Lorenzo Guerra Diez, Clara Barrueco Ramos, Adrián Ranera Málaga, Jose Antonio Alonso-Cadenas, Impact of universal Respiratory Syncytial Virus prophylaxis in Spain Working Group

Published in

European journal of pediatrics. Volume 185. Issue 12. Nov 12, 2026. Epub Nov 12, 2026.

Abstract

Real-world studies have confirmed the high effectiveness of nirsevimab, preventing approximately 80% of RSV bronchiolitis hospitalizations. This study aimed to evaluate the epidemiological and clinical characteristics of RSV bronchiolitis admissions following successful nationwide implementation of nirsevimab. We conducted a retrospective multicenter study across 15 Spanish pediatric emergency departments during the 2024-2025 RSV season. Infants eligible for the RSV prophylaxis, defined as those younger than six months at the start of or during the RSV season, with laboratory-confirmed RSV bronchiolitis requiring hospitalization were included. Patients immunized fewer than seven days before admission or with unknown immunization status were excluded. Epidemiological and clinical data were analyzed according to nirsevimab status, with age-stratified and multivariable analyses performed. Among 366 hospitalized infants with RSV bronchiolitis, 345 were previously healthy. Of these, 165/345 (47.8%) had received nirsevimab. Breakthrough cases were younger than non-breakthrough cases (2.0 months [IQR, 1.1-3.6] vs 5.2 months [IQR, 3.3-6.6]; p < 0.001). Overall, immunized and non-immunized infants showed similar rates of pediatric intensive care unit (PICU) admission (26.7% vs 21.1%; p = 0.2) and length of hospital stay (5 days [IQR, 3-7] vs 5 days [IQR, 4-7]; p = 0.6). After age stratification, clinical characteristics and outcomes remained comparable between groups. In multivariable analyses, no statistically significant association was observed between nirsevimab immunization and PICU admission, advanced respiratory support, or length of hospital stay.
 In-hospital outcomes of RSV bronchiolitis admissions did not differ significantly by immunization status. These findings suggest that, once hospitalization is required, nirsevimab may offer limited additional protection against severe disease.
• Real-world studies have confirmed the high effectiveness of nirsevimab, preventing approximately 80% of RSV bronchiolitis hospitalizations.
• In-hospital outcomes of RSV bronchiolitis admissions did not differ significantly by immunization status. These findings suggest that, once hospitalization is required, nirsevimab may offer limited additional protection against severe disease.

PMID:
43018749
Bibliographic data and abstract were imported from PubMed on 13 Nov 2026.

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