Epidemic Outbreak of Respiratory Syncytial Virus Infection After the end of the Zero-COVID-19 Policy in China: Molecular Characterization and Disease Severity Associated With a Novel RSV-B Clade.

The resurgence of respiratory syncytial virus (RSV) has become a major concern recently. This study aimed to describe the temporal dynamics, genotype variability and disease severity of RSV infection after the end of the Zero-COVID-19 policy in Beijing, China. A total of 905 patients were positive for RSV at National Center for Respiratory Medicine in Beijing from November 2019 to April 2024. Of these, 238 positive samples from different patients were successfully sequenced, 96 of which were identified as the RSV-A and 142 as the RSV-B. Phylogenetic analyses were performed to investigate genetic diversity. The first surge of RSV infection after the end of the Zero-COVID-19 policy was quite intense and occurred out of season, mainly affecting children. The subsequent RSV outbreak had a significant impact among adults. RSV cases were caused by various clades and a new clade B.D.E.1 was identified as the main cause of the epidemic outbreak in adults. Pneumonia in immunocompromised hosts caused by clade B.D.E.1 was more common compared to other clades. Accumulation of substitutions in clade B.D.E.1 could confer a fitness advantage in vivo. However, there was no statistical difference in clinical outcomes between patients infected by clade B.D.E.1 and those infected by other RSV clades. This study addressed the timing and trends of the RSV infections, focusing on epidemic outbreaks, molecular characterization, and disease severity associated with a novel clade B.D.E.1. A more effective prevention strategy for RSV infections in childhood, immunosuppressed adults and elderly might be warranted.