Molecular Characterization of Respiratory Syncytial Virus Infections in Elderly Patients During the 2023-2024 Season in the Era of Nirsevimab Introduction.

Abstract

Respiratory syncytial virus (RSV) can cause severe infections in elderly individuals. Nirsevimab is a novel prophylactic monoclonal antibody, widely used in infants in France during the 2023-2024 season. It may select for resistant RSV variants that, if transmitted in the community, could compromise vaccine efficacy in the elderly. In this study, we analyzed RSV full-length genomes (68% RSV-A, 32% RSV-B) from 125 patients aged >60 years during the 2023-2024 season. Genetic diversity of RSV-F site Ø was low, with no resistance-associated substitutions (RASs) detected. While no RASs were identified, ongoing monitoring is essential to prevent the emergence of resistant variants that could affect vaccine efficacy in the elderly.