Circulation patterns and molecular characteristics of respiratory syncytial virus among hospitalized children in Tianjin, China, before and during the COVID-19 pandemic (2017–2022)

Respiratory syncytial virus (RSV) is the main pathogen that causes hospitalization for acute lower respiratory tract infections (ALRIs) in children. With the reopening of communities and schools, the resurgence of RSV in the COVID-19 post-pandemic era has become a major concern. To understand the circulation patterns and genotype variability of RSV in Tianjin before and during the COVID-19 pandemic, a total of 19,531 nasopharyngeal aspirate samples from hospitalized children in Tianjin from July 2017 to June 2022 were evaluated. Direct immunofluorescence and polymerase chain reaction (PCR) were used for screening RSV-positive samples and subtyping, respectively. Further analysis of mutations in the second hypervariable region (HVR2) of the G gene was performed through Sanger sequencing. Our results showed that 16.46% (3215/19,531) samples were RSV positive and a delayed increase in the RSV infection rates occurred in the winter season from December 2020 to February 2021, with the average RSV-positive rate of 35.77% (519/1451). The ON1, with H258Q and H266L substitutions, and the BA9, with T290I and T312I substitutions, are dominant strains that alternately circulate every 1–2 years in Tianjin, China, from July 2017 to June 2022. In addition, novel substitutions, such as N296Y, K221T, N230K, V251A in the BA9 genotype, and L226I in the ON1 genotype, emerged during the COVID-19 pandemic. Analysis of clinical characteristics indicated no significant differences between RSV-A and RSV-B groups. This study provides a theoretical basis for clinical prevention and treatment. However, further studies are needed to explore the regulatory mechanism of host immune responses to different lineages of ON1 and BA9 in the future.