Outbreak of BA Genotype-Derived RSV-B Lineages in Northeast India: Molecular Epidemiology and Phylogenetic Insights from Dibrugarh, 2022

: Respiratory syncytial virus (RSV) is a major cause of respiratory illness in children, but molecular data from Northeast India remain limited. We investigated an RSV-B outbreak among 239 children aged <5 years in Dibrugarh, Assam, during November-December 2022. RSV-B was detected in 67 (28.0%) samples by real-time RT-PCR. G-gene sequencing of 43 isolates and phylogenetic analysis identified three BA genotype-derived lineages: B.D.E.1 (48.8%), B.D.E.1.2 (37.2%), and B.D.4.1.1 (14.0%). B.D.E.1 and B.D.E.1.2 predominated, comprising 86.0% of sequences. The conserved G:I252T substitution was present across all lineages, with predicted glycosylation differences. These findings provide evidence of RSV-B lineage circulation in Northeast India.