Monitoring effectiveness of nirsevimab immunization against RSV hospitalization using surveillance data: a...

Area of Science:

• Pediatrics
• Infectious Diseases
• Public Health

Background:

• Respiratory syncytial virus (RSV) is a leading cause of severe respiratory infections in infants.
• Nirsevimab is a monoclonal antibody developed for RSV prevention.
• Estimating real-world effectiveness of nirsevimab is crucial for public health strategies.

Purpose of the Study:

• To estimate the effectiveness of nirsevimab in preventing RSV hospitalization in infants in Spain during the 2024/2025 season.
• To analyze nirsevimab effectiveness based on infant birth dates relative to the immunization campaign.
• To identify potential factors influencing nirsevimab effectiveness over time.

Main Methods:

• A test-negative design (TND) using hospital-based respiratory infection surveillance data.
• Systematic RT-PCR testing for RSV in hospitalized infants within 10 days of symptom onset.
• Logistic regression analysis adjusted for relevant covariates to estimate nirsevimab effectiveness.

Main Results:

• Overall nirsevimab effectiveness was 65.5% (95% CI: 45.2 to 78.3) against RSV hospitalization.
• Effectiveness was comparable for infants born before (63.6%) and after (70.4%) the campaign start.
• An early decrease in effectiveness was noted with increasing time since immunization and age, though with wide confidence intervals.

Conclusions:

• Nirsevimab shows significant effectiveness in preventing RSV hospitalizations in Spanish infants.
• The study highlights potential early waning of effectiveness and methodological challenges in TND for dynamic newborn populations.
• Further research is needed to understand age-period-cohort effects and refine TND implementation for nirsevimab effectiveness studies.