Delayed respiratory syncytial virus outbreak in 2020 in Taiwan was correlated with two novel RSV-A genotype ON1 variants

Background Human respiratory syncytial virus (RSV) is a leading pathogen of acute respiratory tract disease among infants and young children. Compared with previous seasons, RSV outbreaks in Taiwan during the 2020-2021 season were delayed because of COVID-19 mitigation measures. We conducted this study to determine the association of viral factors with clinical characteristics of preschool children with RSV infection. Methods We performed a molecular epidemiology analysis of RSV among inpatient preschool children in Taiwan. In 80 nasopharyngeal samples positive for RSV, we sequenced and analyzed viral genotypes according to patient data. Patients' clinical data were obtained from medical files, and their clinical profiles were compared with those of RSV cases recorded during the 2014-2017 seasons. Results Phylogenetic analysis revealed that among the RSV-positive samples, all RSV strains identified during the 2020-2021 season belonged to the ON1 genotype. Most of the Taiwan ON1 strains were categorized into two well-supported clusters with distinct G protein amino acid substitution patterns that had never been demonstrated previously. Furthermore, the proportion of cases among children aged >24 months increased (P < 0.001). Compared with patients infected during the 2014-2017 seasons, patients infected during the 2020-2021 season were hospitalized for shorter days from hospital admission to dereference (P = 0.004) and had a greater need for oxygen supplements (P = 0.021) and systemic steroid therapy (P = 0.026). Conclusion The delayed 2020-2021 RSV outbreak in Taiwan was caused by two novel RSV ON1.1 variants. How the change in RSV epidemiology affects future RSV outbreaks warrants exploration.