RSV-B Resistance to Nirsevimab Detected in Infants, Highlighting Need for Genomic Surveillance
A study conducted in France has identified resistance to the monoclonal antibody nirsevimab in respiratory syncytial virus B (RSV-B) among infants with breakthrough infections. The POLYRES-2 study analyzed over 1,000 RSV cases, revealing that resistance was primarily found in RSV-B, with 12.5% of breakthrough infections showing resistance-associated mutations. These mutations were not present in infants who had not received nirsevimab, suggesting they emerged under selective pressure from the prophylaxis. Despite these findings, the overall effectiveness of nirsevimab remains high, with resistance confined to a small proportion of cases. 
