Nirsevimab Effectiveness Against RSV-Related Hospitalisations in Children Under 24 Months: A Test-Negative Case-Control Study in Portugal, 2024-2025

Influenza Other Respir Viruses. 2025 Dec;19(12):e70186. doi: 10.1111/irv.70186.

Abstract

We assessed Nirsevimab effectiveness (NE) against respiratory syncytial virus (RSV)-related hospitalisation in eligible children (< 2 years) using a test-negative case-control design within the VigiRSV network (weeks 43/2024 to 16/2025). Among 341 participants (median age: 2 months; 91.2% without known chronic condition), 137 (40.2%) tested RSV-positive. Adjusted NE against RSV-related hospitalisation was 78.5% (95%CI: 59.3-89.0). Sensitivity analyses confirmed the robustness of the results. These findings support Nirsevimab's effect in a predominantly healthy infant population and contribute to informing public health decisions for RSV immunisation.

Keywords: RSV‐related hospitalisations; children; effectiveness; nirsevimab.

MeSH terms

  • Antibodies, Monoclonal, Humanized* / therapeutic use
  • Antiviral Agents* / therapeutic use
  • Case-Control Studies
  • Female
  • Hospitalization* / statistics & numerical data
  • Humans
  • Infant
  • Infant, Newborn
  • Male
  • Portugal / epidemiology
  • Respiratory Syncytial Virus Infections* / drug therapy
  • Respiratory Syncytial Virus Infections* / epidemiology
  • Respiratory Syncytial Virus Infections* / prevention & control
  • Respiratory Syncytial Virus, Human / drug effects

Substances

  • Antiviral Agents
  • Antibodies, Monoclonal, Humanized