Evolution of circulating respiratory syncytial virus lineages before and after the COVID-19 pandemic, 2017-2024, Taiwan.

This study examines the genomic characteristics of the RSV G protein from 2017 to 2024, describing the progression of RSV lineages in Taiwan before and after the pandemic. A total of 428 RSV G ectodomain sequences were analyzed, with the sequence distribution by period as follows: 130 (2017-2019), 86 (2020-2021), 102 (2022), 58 (2023), and 52 (2024). Since 2020, RSV A and B have alternated in predominance, resulting in four separate epidemics in 2020, 2022, 2023, and 2024. All identified RSV strains in Taiwan are derived from the GA2.3.5 and GB5.0.5a genotypes. RSV-A showed complex lineage dynamics, with A.D and A.D.3 dominating pre-pandemic, A.D.3 exclusively circulating in 2020-2022, and the emergence of A.D.5.2 in 2023. RSV-B demonstrated lineage turnover from the predominant B.D.4.1.1 pre-pandemic to the emerging B.D.E.1 from 2022 onwards. The evolutionary rates were estimated at 3.002 × 10-3 substitutions/site/year and 3.63 × 10-3 substitutions/site/year for RSV-A and RSV-B, respectively. Twenty-two amino acid substitutions were found in the G protein ectodomains of both RSV-A and RSV-B, mainly in hypervariable regions, reflecting lineage changes over time. The data indicate that the COVID-19 pandemic significantly affected RSV circulation patterns and evolutionary dynamics in Taiwan. Furthermore, alterations in population immunity may have played a role in shaping the evolution and alternation of RSV lineages within the region.