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Updated: Jun 23, 2025
An Improved and High Throughput Respiratory Syncytial Virus RSV Micro-neutralization Assay
Published on: January 26, 2019
Nirsevimab immunization's real-world effectiveness in preventing severe bronchiolitis: A test-negative case-control
Marta Agüera1, Aleix Soler-Garcia1,2,3, Carme Alejandre4
1Pediatrics Department, Hospital Sant Joan de Déu, Barcelona, Spain.
Insights
Nirsevimab significantly reduced hospitalizations for respiratory syncytial virus (RSV) lower respiratory tract infections in infants. This real-world evidence supports nirsevimab
Area of Science:
- Pediatric Infectious Diseases
- Immunology
- Public Health
Background:
- Respiratory Syncytial Virus (RSV) bronchiolitis is a major cause of infant hospitalization.
- Nirsevimab, an antibody targeting RSV, has shown promise in clinical trials.
- Catalonia and Andorra implemented nirsevimab immunization strategies for infants in 2023-2024.
Purpose of the Study:
- To evaluate the real-world effectiveness of nirsevimab in preventing RSV bronchiolitis hospitalizations.
- To assess nirsevimab's impact on severe RSV disease in infants.
- To compare outcomes between immunized and non-immunized infants.
Main Methods:
- A test-negative case-control study was conducted across three hospitals.
- Infants under 12 months admitted with bronchiolitis and tested for RSV were included.
- Multivariate models estimated effectiveness against RSV hospitalization and severe disease.
Main Results:
- Nirsevimab demonstrated 81.0% effectiveness against RSV-lower respiratory tract infection hospitalization.
- Effectiveness in preventing severe disease (NIV/CMV) was 85.6%.
- Immunized infants had significantly lower RSV detection rates (37% vs 75%).
Conclusions:
- Nirsevimab provides real-world protection against RSV hospitalization and severe disease in infants.
- The immunization program showed high effectiveness in a real-world setting.
- No increased risk of viral coinfections or clinical severity was observed in immunized infants.
Background:
Several clinical trials have shown that nirsevimab, an antibody targeting the respiratory syncytial virus (RSV), reduces RSV bronchiolitis requiring admission. In 2023-2024, Catalonia and Andorra adopted immunization strategies for children <6 months and those born during the epidemic season. This study evaluates the effectiveness of nirsevimab in preventing hospitalizations from RSV bronchiolitis.
Methods:
In the epidemic season of 2023-2024, a test-negative case-control study was conducted in three hospitals from Catalonia and Andorra. Patients <12 months old admitted with bronchiolitis and tested for RSV using molecular microbiology tests were included. The effectiveness in preventing RSV bronchiolitis hospitalization and severe disease was estimated using multivariate models. Comparisons between immunized, non-immunized, and non-eligible patients were made in prospectively collected epidemiological, clinical, and microbiological variables.
Results:
Two hundred thirty-four patients were included. RSV was detected in 141/234 (60.2%), being less common in the immunized group (37% vs 75%, p < .001). The rate of immunized patients among those eligible was 59.7%. The estimated effectiveness for RSV-associated lower respiratory tract infection was 81.0% (95% confidence interval: 60.9-90.7), and for preventing severe disease (the need for NIV/CMV), 85.6% (41.7-96.4%). No significant differences by immunization status were observed in patients with RSV concerning viral coinfections, the need for NIV/CMV or length of hospital stay.
Conclusions:
This study provides real-world evidence of the effectiveness of nirsevimab in preventing RSV-lower respiratory tract infection hospitalization and severe disease in infants during their first RSV season following a systematic immunization program. Immunized patients did not exhibit a higher rate of viral coinfections nor differences in clinical severity once admitted.
