Nirsevimab Immunization to Prevent Pediatric RSV Hospitalizations

Importance: Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infections in infants and young children, imposing a substantial burden on health care systems. Nirsevimab, a long-acting monoclonal antibody, has shown high efficacy in clinical trials, and modeling studies suggest it may be cost-effective; however, real-world evidence on its cost-effectiveness in European health care settings remains limited. Objective: To evaluate the real-world cost-effectiveness of nirsevimab immunization in preventing pediatric hospitalizations due to RSV. Design, setting, and participants: This multicenter, observational, real-world cost-effectiveness analysis was conducted between October 1, 2022, and March 31, 2025. Precampaign data were modeled using Poisson regression models to estimate expected hospitalizations in the absence of immunization. Data were gathered from 19 pediatric hospitals distributed across 11 Italian regions, from northern to southern areas. Included were all pediatric hospitalizations with RSV-specific International Classification of Diseases, Ninth Revision, Clinical Modification discharge diagnoses recorded at participating hospitals between October 1, 2022, and March 31, 2025. Exposures: Regional nirsevimab immunization campaigns with varying start dates and eligibility criteria, implemented between October 2024 and January 2025. Main outcomes and measures: Effectiveness, expressed as hospitalizations averted (ΔE), and incremental costs (ΔC) were estimated from the Italian National Health Service perspective. Cost-effectiveness ratios (CERs = ΔC/ΔE) were calculated for each center. Results: During the 2024 to 2025 season, 5924 RSV-related hospitalizations were recorded in children 18 years and younger across 19 centers. Observed admissions were consistently lower than model-based counterfactual predictions in most centers. Immunization averted between 6 and 151 admissions per center, corresponding to a rate of 83 and 1162 per 100 000 children. Incremental costs were negative in most centers, indicating cost savings ranging from -€10 924 (US $12 562.60) to -€266 954 (US $306 997.10) per center. Corresponding cost-effectiveness ratios were negative (-€1071 [US $1231.65] and -€1682 [(US $1934.30]), reflecting a cost-saving intervention. In 2 centers with late initiation and restricted eligibility, immunization was associated with higher costs relative to the number of hospitalizations prevented, with incremental costs of €19 715 (US $22 672.25) and €81 454 (US $93 672.10). Sensitivity analyses confirmed the robustness of results. Conclusions and relevance: Results of this Italian multicenter, real-world economic evaluation suggest that nirsevimab immunization was both clinically effective and cost saving from a health system perspective. Timing and eligibility of immunization strongly influenced cost-effectiveness, highlighting the importance of early and broad rollout strategies to maximize clinical and economic benefits.