Epidemiology of human RSV in Taiwan, 2018-2024

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infections in infants and older adults worldwide. This retrospective study investigated the epidemiology and molecular characteristics of RSV in Taiwan from 2018 to 2024 using data from the National Community Virus Surveillance System, which encompassed the coronavirus disease 2019 (COVID-19) pandemic period. Among 74,773 samples collected from patients with suspected respiratory viral infections, 1,224 samples tested positive for RSV, yielding an overall detection rate of 1.6%. RSV circulation was markedly disrupted during the COVID-19 pandemic, with no cases being detected during periods of stringent public health interventions and delayed outbreaks observed in late 2020 and 2023. Following the relaxation of nonpharmaceutical interventions, RSV seasonality shifted, with altered epidemic timing and changes in age distribution being observed. Most infections occurred in children younger than 5 years of age (92.6%), and RSV positivity varied significantly across age groups but not between sexes. Among the 1,224 isolates, 463 were randomly selected for glycoprotein (G) gene sequencing. The results revealed that RSV-A accounted for the majority (81.6%) of the tested isolates and were clustered within the A.D lineage, with A.D.3 being the dominant clade. The remaining strains were determined to be RSV-B, which were classified within the B.D lineage, with B.D.E.1 being observed as the dominant clade. The emergence of multiple RSV subclades during the study period indicates ongoing viral evolution in Taiwan. These findings demonstrate substantial shifts in RSV epidemiology following the COVID-19 pandemic and highlight viral evolution and clade replacement. Continued molecular surveillance is essential to monitor epidemiological trends and inform vaccination and prevention strategies.