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Updated: Sep 18, 2025
An Improved and High Throughput Respiratory Syncytial Virus RSV Micro-neutralization Assay
Published on: January 26, 2019
RSV bronchiolitis: a disease only for those who do not receive prophylaxis
A Villani1,2, L Antilici3, A M C Musolino1
1Hospital University Pediatrics Clinical Area, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy.
Insights
Nirsevimab significantly reduced RSV bronchiolitis hospitalizations in infants, especially newborns. Early and widespread immunization is key to maximizing benefits and preventing severe respiratory syncytial virus cases.
Area of Science:
- Pediatrics
- Infectious Diseases
- Public Health
Background:
- Respiratory syncytial virus (RSV) is a major cause of infant hospitalization.
- Nirsevimab, approved in 2023, offers universal prophylaxis against RSV bronchiolitis.
- Italy introduced nirsevimab in the 2024-2025 season with regional variations.
Purpose of the Study:
- To evaluate the effectiveness of nirsevimab in reducing RSV bronchiolitis hospitalizations in Lazio, Italy.
- To assess the impact of delayed introduction and varying vaccination coverage on nirsevimab's effectiveness.
Main Methods:
- Retrospective analysis of RSV bronchiolitis hospitalizations before and after nirsevimab introduction in Lazio.
- Comparison of hospitalization rates and clinical outcomes between immunized and non-immunized infants.
- Analysis of nirsevimab's impact on different infant groups (newborns vs. catch-up).
Main Results:
- Overall reduction of 43% in RSV bronchiolitis hospitalizations in Lazio.
- Newborns immunized at birth showed an 82.7% reduction in hospitalizations.
- Catch-up group had lower-than-expected benefits (29% reduction).
- Immunized infants required significantly less oxygen support (42.9% vs. 82.4%).
Conclusions:
- Universal infant immunization with nirsevimab is a breakthrough in managing bronchiolitis.
- Early and widespread nirsevimab administration is critical for maximizing hospitalization reduction.
- Targeted strategies may be needed to improve catch-up vaccination coverage and benefits.
Abstract:
Bronchiolitis is a leading cause of hospitalization in infants, with RSV being the primary pathogen. In 2023, nirsevimab was approved for universal prophylaxis, demonstrating high effectiveness in reducing RSV-related hospitalizations. In Italy, nirsevimab was introduced in the vaccination schedule only during the current 2024-2025 epidemic season, with significant regional differences. In our region, Lazio, nirsevimab was introduced in late November 2024, leading only to a 43% overall reduction in RSV bronchiolitis hospitalizations compared to the previous season. The highest impact was observed in newborns immunized at birth (- 82.7%), while the catch-up group showed lower-than-expected benefits (- 29%). Immunized infants had significantly lower oxygen requirements (42.9% vs. 82.4% in non-immunized) and resulted to be approximately seven times more likely not to require oxygen compared to non-immunized patients.
Conclusion:
Universal infant immunization against RSV marks a significant breakthrough in the natural history of bronchiolitis, and early and widespread nirsevimab administration appears to be crucial in minimizing RSV's hospitalizations.
What Is Known:
• Nirsevimab was approved in 2023 for the universal prophylaxis against RSV bronchiolitis. • Nirsevimab was was introduced in the Italian vaccination schedule only during the current 2024-2025 epidemic season, with significant regional differences.
What Is New:
• In Lazio, Italy, the delayed introduction of nirsevimab in November 2024 and the reduced vaccination coverage of the catch-up group resulted in a lower-than-expected reduction in RSV bronchiolitis hospitalizations. • Early and widespread administration of nirsevimab is crucial to maximizing its benefits and reducing severe RSV cases.
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