Impact of Seasonal Nirsevimab Administration in Infants Born During the RSV Circulation Period on RSV-Related

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Susanna Esposito1,2, Matteo Puntoni3, Giuseppe Maglietta3

  • 1Pediatric Clinic, University-Hospital of Parma, 43126 Parma, Italy.

Vaccines
|February 26, 2026
PubMed

Insights

Seasonal nirsevimab significantly reduced respiratory syncytial virus (RSV) hospitalizations in young infants. This long-acting antibody provides season-long protection, lowering infant hospital admission rates effectively.

Area of Science:

  • Pediatrics
  • Infectious Diseases
  • Public Health

Background:

  • Respiratory syncytial virus (RSV) is a major cause of infant hospitalization, particularly in the first months of life.
  • Intensified RSV circulation observed globally post-COVID-19 pandemic.
  • Nirsevimab, a long-acting monoclonal antibody, offers season-long protection against RSV after a single dose.

Purpose of the Study:

  • To evaluate the population-level impact of seasonal nirsevimab administration on RSV-related hospitalizations in young infants in Italy.
  • To assess the effectiveness of nirsevimab for infants born during the RSV circulation period.

Main Methods:

  • Population-based observational study using regional hospital discharge records (Emilia-Romagna, Italy, Jan 2017-Apr 2025).
  • Analysis focused on RSV seasons (Oct-Mar) and infants ≤180 days old, identifying RSV hospitalizations via ICD-9-CM codes.
  • Incidence rate ratios (IRRs) compared hospitalization rates in the post-nirsevimab season (2024-2025) with pre-nirsevimab (2023-2024) and pre-COVID (2018-2019) seasons.

Main Results:

  • A substantial reduction in RSV hospitalizations was observed in the post-nirsevimab season (252 cases) compared to pre-nirsevimab (753 cases) and pre-COVID (551 cases) seasons.
  • Nirsevimab use was associated with significantly lower hospitalization rates: IRR 0.36 vs. pre-nirsevimab season and IRR 0.52 vs. pre-COVID season.
  • Reductions were consistent across epidemic months and most pronounced in infants aged 0-4 months.

Conclusions:

  • Seasonal nirsevimab administration to infants during RSV circulation markedly reduced RSV-related hospitalizations in early infancy.
  • Findings support the efficacy of targeted, seasonally timed infant immunoprophylaxis for population-level RSV prevention.
  • Nirsevimab represents an effective strategy for mitigating the burden of RSV in vulnerable young infants.
Abstract

Keywords:
RSV preventionimmunoprophylaxismonoclonal antibodiesnirsevimabpediatric infectious diseasesrespiratory syncytial virus

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