摘要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 immunoflu-orescence 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 per-formed 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.