National real-life impact of prevention with nirsevimab on infants' RSV hospitalizations in Belgium

Abstract

Background Since 2023, two preventive tools (monoclonal antibodies, nirsevimab, and preF maternal vaccine) were approved to protect infants against severe RSV infections. During winter 2024-2025, nirsevimab started to be administered in Belgium to infants < 6 months old encountering their first RSV season. We aim to evaluate on a national scale the impact of RSV prevention in the pediatric hospital setting. Method This survey pooled data from two surveillance systems: the prospective SARI (Severe Acute Respiratory Infection) surveillance (6 hospitals) and the retrospective RSVPed study (25 hospitals). Both used the same case definition and clinical questionnaire to record RSV hospitalizations in children < 5 years. Seasonal incidences and clinical data were compared between seasons 2023-2024 (pre-prevention) and 2024-2025 (first year of prevention). Results Our study covered 47% of all pediatric beds in Belgium. We demonstrated a reduction of 39% in pediatric RSV-related hospitalizations and of 57% in RSV-related admissions to intensive care units during 2024-2025 compared to 2023-2024. Incidences decline mainly concerned infants < 6 months, without changes in older age groups. Furthermore, savings in health care resources were observed through shorter length of stay and significantly less use of non-invasive ventilatory support and nutritional support among hospitalized cases in 2024-2025. Conclusion Following implementation of nirsevimab, a substantial reduction in RSV paediatric burden was observed in Belgium. However, efforts should be made to increase the uptake of preventive tools in our country to achieve better effectiveness. This study also highlights the major role of a national network to monitor efficacy of prevention over time.Clinical trial number Not applicable.