Isolation, identification and whole genome sequence analysis of influenza B virus from Shanghai during 2023–2024

Influenza B virus, a member of the Orthomyxoviridae family, is a significant contributor to global respiratory infections alongside influenza A virus. This study investigated the prevalence and genomic characteristics of influenza B virus during the 2023–2024 season in Shanghai, China. Among 174 clinical samples collected from the Nanxiang Branch of Ruijin Hospital, the positivity rate for influenza B virus was 62.36%. Genomic analysis revealed that all characterized isolates belonged to the B/Victoria lineage and were classified within subclade C.5.7, corresponding to the legacy designation V1A.3a.2. No B/Yamagata lineage strains were detected. Comparative genomic analysis further revealed close genetic similarity between the Shanghai isolates and strains from Shanxi Province, suggesting a potential geographical or evolutionary relationship. These findings highlight the substantial activity of influenza B virus in Shanghai during the study period and underscore the importance of continued genomic surveillance to monitor viral evolution and inform public health strategies. The Influenza B positivity rate was 62.36% during the 2023–2024 season in Shanghai, indicating significant activity of the virus in this region. Seven Influenza B strains were successfully isolated from 174 positive samples analyzed. All positive samples belonged to the B/Victoria lineage, while no B/Yamagata lineage strains were detected. Whole genome sequencing revealed that the isolated strains belong to the B/Victoria. The hemagglutinin (HA) genes of these strains were classified within clade C.5.7 of the B/Victoria lineage, corresponding to the legacy designation V1A.3a.2. Comparative analysis showed close genetic similarity with sequences from Shanxi, suggesting potential geographical or evolutionary connection.