Waning protection of long-acting RSV monoclonal antibodies in infants: a Bayesian analysis of clesrovimab and nirsevimab trial data

Clesrovimab and nirsevimab are long-acting monoclonal antibodies used to prevent respiratory syncytial virus (RSV) disease in infants. Researchers used Bayesian analysis to examine how their efficacy declines during the first year of life. Clesrovimab efficacy against RSV lower respiratory tract infections declined from 60.7% shortly after administration to 38.3% after six months. Against RSV-associated hospitalization, it declined from 87.1% to 49.6%. For nirsevimab, corresponding values were 86.9% declining to 53.8% against infections and 77.5% declining to 49.7% against hospitalization. After accounting for differences in RSV exposure timing and endpoint definitions between trials, researchers found no evidence of a difference in efficacy or waning between the two antibodies.