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Multicenter Study
. 2025 Mar 5;184(3):229.
doi: 10.1007/s00431-025-06050-7.

Effectiveness of nirsevimab in reducing hospitalizations in emergency departments due to bronchiolitis among infants under 3 months: a retrospective study

Alexis Marouk  1   2 , Bernadette Verrat  3 , Isabelle Pontais  3 , Dumitru Cojocaru  4 , Hélène Chappuy  5   6 , Irina Craiu  7 , Pauline Quagliaro  8 , Vincent Gajdos  9 , Valérie Soussan-Banini  10 , Yves Gallien  3 , Anne-Laure Feral-Pierssens  11   12
Affiliations
Multicenter Study

Effectiveness of nirsevimab in reducing hospitalizations in emergency departments due to bronchiolitis among infants under 3 months: a retrospective study

Alexis Marouk et al. Eur J Pediatr. .

Abstract

Respiratory syncytial virus (RSV) is a leading cause of infant morbidity. France has implemented a national campaign using nirsevimab to prevent RSV-related infections in infants. This study assessed its effectiveness in preventing hospitalization due to bronchiolitis in emergency department (ED). This retrospective study was conducted among six pediatric EDs in the Greater Paris area, France, and included infants aged < 3 months with a clinical diagnosis of bronchiolitis during the 2023-2024 RSV epidemic season. The primary outcome was hospitalization after the ED visits. The association with nirsevimab immunization was assessed using a multiple logistic model adjusted for potential confounding factors, with missing data handled using random forest imputation. Secondary analyses examined the risk of admission to the pediatric intensive care unit (PICU), RSV positivity, and subgroup analyses of prematurity, neonates, and deprivation using the FDep index (area-based measure of social deprivation in France). Between October 2 and December 31, 2023, 739 infants were included in the study. A total of 531 (72%) patients had a documented nirsevimab immunization status, and 402 (54%) were hospitalized following a bronchiolitis diagnosis. Nirsevimab showed 53.5% adjusted effectiveness in reducing hospitalizations (95% CI 34.1-67.3). Sensitivity analyses of complete-case data and propensity score matching yielded similar results. Nirsevimab also resulted in 51.1% reduction in PICU admissions (95% CI 10.7-74.3) and 79.6% reduction in RSV positivity (95% CI 68.0-87.1). The protective effect of immunization was consistent for preterm infants, neonates, and deprived groups, though the results were not statistically significant in these smaller subgroups.

Conclusions: Immunization with nirsevimab reduced hospitalization following an ED visit for bronchiolitis among infants aged < 3 months.

What is known: • Nirsevimab reduces the risk of bronchiolitis-related hospitalizations in clinical trials. • Real-world data from the immunization campaign in France remain limited.

What is new: • Nirsevimab showed 53.5% (95% CI 34.1-67.3) adjusted effectiveness in reducing hospitalizations for all-cause bronchiolitis in infants aged < 3 months in emergency departments. • Analyses included social deprivation and highlighted potential disparities in immunization access.

Keywords: Bronchiolitis; Immunization; Nirsevimab; Pediatric; RSV.

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Conflict of interest statement

Declarations. Ethical approval: This study was performed in line with the principles of the Declaration of Helsinki. The study protocol was reviewed and approved by the local ethics committee: Comité Local d’Ethique pour la Recherche Clinique des Hôpitaux Universitaires Paris Seine-Saint-Denis (CLEA) (date 26/01/2024, protocol number: CLEA-2024-n°359). Consent to participate: The research was conducted in compliance with the General Data Protection Regulation for the reuse of health data in Europe and the French Data Protection Authority (registration number: 2234142). The study was registered on the Health Data Hub (No. 17697713) prior to data collection. Parents were informed about the potential use of data for research purposes through general information provided at the point of care and publicly available information. Conflicts of interest: The authors declare no competing interests.

References

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