Nirsevimab immunization’s real-world effectiveness in preventing severe
bronchiolitis: a test-negative case-control study
Abstract
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 234 patients were
included. RSV was detected in 141/234(60.2%), being less common in the
immunized group (37% vs 75%, p<0.001). 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
co-infections, 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-LRTI 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 co-infections nor differences in clinical severity
once admitted.