Association between nirsevimab coverage and pediatric emergency department visits for bronchiolitis in 12 European countries: An interrupted time-series analysis

The introduction of nirsevimab aimed to prevent RSV bronchiolitis in infants across Europe. However, the extent of bronchiolitis reduction varied significantly from country to country. To investigate whether nirsevimab coverage among target populations influenced these differences, a multinational study analyzed data from 27 pediatric emergency departments in 12 European countries spanning from January 2018 to March 2024.

Researchers examined the correlation between nirsevimab coverage and bronchiolitis cases, comparing them to urinary tract infections as a control outcome. In total, 107,088 bronchiolitis cases were included in the analysis.

Findings revealed substantial variability in bronchiolitis reduction across regions and age groups, ranging from a minor increase of +0.6% to a dramatic decrease of −61.0%. Notably, strong correlations were observed between nirsevimab coverage and bronchiolitis reduction across all age groups and regions (rho = -0.86, p = 0.001).

In contrast, bronchiolitis trends remained stable in control countries, as did rates of urinary tract infections. The study acknowledges its limitations as an ecological analysis, noting that causality cannot be definitively established and unmeasured regional differences may have contributed to the observed variability.

The study concludes that nirsevimab coverage is a key factor associated with bronchiolitis reduction across age groups and European regions. Implementation choices in different countries likely influenced coverage rates, suggesting that the benefits of nirsevimab depend not only on its intrinsic effectiveness but also on how effectively it is delivered and utilized within each region.