INTRODUCTION: The epidemic pattern of the Respiratory syncytial virus (RSV) has changed during the COVID-19 pandemic. To analyze the epidemic pattern of RSV infection and explore the fluctuations of immunity. METHODOLOGY: Pediatric inpatients diagnosed with RSV infection or RSV pneumonia from January 2019 to August 2023 in a tertiary hospital were retrospectively included. The children were divided into three groups: before the implementation of non-pharmaceutical interventions (NPIs) group, during the implementation of NPIs group, and after the lifted NPIs group. RESULTS: A total of 462 children were included in this study. During the implementation of NPIs, there were almost no RSV hospitalizations from February to October 2020. In May 2023, the number of children infected with RSV increased dramatically. The RSV infected children in after the lifted NPIs group was mainly ≥ 3 years old. RSV mixed infections (56.93%) were slightly more common than RSV single infection (43.07%). The levels of IgG, IgA, IgM, and CD3+%, CD8+% during the implementation of NPIs and after the lifted NPIs groups were lower than those in the other group of infants 0-6 months old, and the levels of CD3+ % and CD3 + CD4+ % in children 7-12 months old were found to be similar. CONCLUSIONS: After the lifted NPIs, the RSV epidemic season was delayed to spring and summer. Humoral immunity and part of the cellular immunity in infants varies before and after NPIs. We pay close attention to the surveillance data of RSV to prevent RSV infection.