Clinical Report: Variable Impact of Regional Nirsevimab Vaccination Strategies

Overview

This study described pediatric RSV hospitalization trends over six seasons and assessed early population-level changes during the 2024–2025 nirsevimab rollout across Italian regions with different eligibility criteria and implementation timelines.

Background

Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory tract infection and hospitalization among infants and young children worldwide. Nirsevimab, a long-acting monoclonal antibody targeting the RSV fusion protein, expanded prevention beyond the limited use of palivizumab in selected high-risk infants. Italy expanded nirsevimab implementation nationwide during 2024–2025, although regional strategies differed.

Data Highlights

• The study included 10,915 RSV-related hospitalizations among patients younger than 18 years across 19 pediatric units in 12 Italian regions.

• RSV-related hospitalizations decreased by 43.6% overall during 2024–2025 compared with the three-season preimmunization mean.

• Groups A and B had modeled hospitalization ratios of 0.40 and 0.28, respectively; single-center Group F had a ratio of 0.24, with an indicative interval.

• Influenza hospitalizations increased by 93.7% across the same centers while RSV hospitalizations declined.

Key Findings

• Nirsevimab was approved by the European Medicines Agency in 2022 and authorized nationally by the Italian Medicines Agency in 2023.

• Participating centers were divided into seven groups based on regional birth month-based eligibility criteria and campaign timing.

• The largest reductions among multicenter groups occurred in Groups A and B, which had broader eligibility and earlier implementation.

• Groups C, D, and E had more modest reductions, while Group G showed no clear change after baseline instability was considered.

• The study found a temporal association between nirsevimab implementation and fewer RSV-related hospitalizations but could not establish causation or compare regional effectiveness.

Clinical Implications

The findings are compatible with timely implementation and broader eligibility contributing to larger population-level reductions in RSV hospitalizations. However, the absence of age-specific data, individual immunization status, and regional uptake estimates prevents direct attribution of the reductions to immunized infants. Continued surveillance, harmonized coverage monitoring, and age-specific analyses are needed to inform future RSV prevention policies.

Conclusion

The 2024–2025 nirsevimab rollout was temporally associated with reduced pediatric RSV-related hospitalizations in Italy, with heterogeneous changes across regional strategy groups. The uncontrolled before-and-after design cannot establish causation or determine the comparative effectiveness of regional strategies.

Related Resources & Content

1. Primary study: “Heterogeneous reduction in pediatrics RSV hospitalizations following regional nirsevimab immunization strategies: a multicenter study” — Federica Attaianese, Sandra Trapani, and colleagues; International Journal of Infectious Diseases, Volume 171 (2026), article 109076; accepted August 23, 2026.

2. Nirsevimab efficacy: “Efficacy of nirsevimab against respiratory syncytial virus lower respiratory tract infections in preterm and term infants, and pharmacokinetic extrapolation to infants with congenital heart disease and chronic lung disease: a pooled analysis of randomised controlled trials” — Simões EAF, Madhi SA, Muller WJ, and colleagues; The Lancet Child & Adolescent Health, Volume 7, Issue 3 (2023), pages 180–189.

3. Preterm-infant prevention: “Single-dose nirsevimab for prevention of RSV in preterm infants” — Griffin MP, Yuan Y, Takas T, Domachowske JB, Madhi SA, Manzoni P, and colleagues; The New England Journal of Medicine, Volume 383, Issue 5 (2020), pages 415–425.

4. RSV hospitalization: “Nirsevimab and hospitalization for RSV bronchiolitis” — Assad Z, Romain AS, Aupiais C, Shum M, Schrimpf C, Lorrot M, and colleagues; The New England Journal of Medicine, Volume 391, Issue 2 (2024), pages 144–154.

5. Universal prophylaxis: “Effectiveness and impact of universal prophylaxis with nirsevimab in infants against hospitalisation for respiratory syncytial virus in Galicia, Spain: initial results of a population-based longitudinal study” — Ares-Gómez S, Mallah N, Santiago-Pérez MI, Pardo-Seco J, Pérez-Martínez O, Otero-Barrós MT, and colleagues; The Lancet Infectious Diseases, Volume 24, Issue 8 (2024), pages 817–828.

6. Immunization recommendations: “Use of nirsevimab for the prevention of respiratory syncytial virus disease among infants and young children: recommendations of the Advisory Committee on Immunization Practices—United States, 2023” — Jones JM, Fleming-Dutra KE, Prill MM, Roper LE, Brooks O, Sánchez PJ, and colleagues; Morbidity and Mortality Weekly Report, Volume 72, Issue 34 (2023), pages 920–925.

7. Targeted infant immunization: “Effectiveness of a targeted infant RSV immunization strategy (2024–2025): a multicenter matched case-control study in a high-surveillance setting” — Attaianese F, Trapani S, Agostiniani R, Ambrosino N, Bertolucci G, Biasci P, and colleagues; Journal of Infection, Volume 91, Issue 3 (2025), article 106600.

8. Italian hospitalization trends: “Disrupted seasonality of respiratory viruses: retrospective analysis of pediatric hospitalizations in Italy from 2019 to 2023” — Palmas G, Trapani S, Agosti M, Alberti I, Aricò M, Azzari C, and colleagues; The Journal of Pediatrics, Volume 268 (2024), article 113932.

9. Hospitalization prevention: “Nirsevimab immunization to prevent pediatric RSV hospitalizations” — Attaianese F, Carreras G, Trapani S, Alberti I, Aricò M, Attanasi M, and colleagues; JAMA Pediatrics (2026).