Mucosal nirsevimab levels in respiratory syncytial virus breakthrough bronchiolitis

This study highlights the crucial role of sufficient mucosal nirsevimab in protecting infants against RSV bronchiolitis. The mechanisms leading to breakthrough infections despite nirsevimab administration remain incompletely understood. Although impaired mucosal antibody transfer is one potential explanation, other factors such as inadvertent underdosing, increased nirsevimab loss due to underlying conditions, rapid degradation of the monoclonal antibody, production of inhibiting anti-drug antibodies, insufficient serum levels, or RSV strains harbouring resistance mutations cannot be excluded. Further research is necessary to elucidate these mechanisms and optimise the effectiveness of nirsevimab in preventing RSV bronchiolitis.