The Changed Endemic Pattern of Respiratory Syncytial Virus Infections in Pediatric Patients With the Relaxation of NPIs in Beijing, China, 2022−2023

With the cancellation of non-pharmaceutical interventions (NPIs) since December 26, 2022, in Beijing, it is essential to update the endemic pattern of respiratory syncytial virus (RSV) in pediatric patients. Respiratory specimens were collected from hospitalized children with acute respiratory infections (ARIs) from January 2022 to December 2023 in Beijing for multiple pathogen screening. Then, specimens positive for RSV were subtyped by PCR and genotyped by G gene sequencing and phylogenetic analysis with Mega X. The clinical data of children only positive for RSV were compared using SPSS 22.0 software. Among 7131 specimens enrolled, there were 9.21% (203/2205) and 10.74% (529/4926) positive for RSV before and after the cancellation of NPIs, respectively. The expected RSV endemic season from November 2022 to March 2023 disappeared, and the RSV positive rates kept in 0.00% in January and February 2023, which were then increased rapidly to 14.81% in April and 24.60% in May, and to 14.35% and 18.18% again in November and December 2023, with the dominant subtype of RSV transferred from A to B in November 2023. Phylogenetic analysis revealed that clusters ON1.2 and BA9.3, especially, a new variant RSV-B-BA9-954bp, only showed in specimens collected after the cancellation of NPIs. Higher proportion of children aged 3-6 years and over 6 years which increased from 10.56% to 21.41%, and from 3.33% to 7.59%, respectively, and less severe pneumonia cases which decreased from 50.00% to 17.86%, were observed after the cancellation of NPIs. With the cancellation of NPIs, a delayed endemic season of RSV was shown in April and May 2023, with new clusters of ON1.2 and BA9.3, especially a new variant (RSV-B-BA9-954bp), a high proportion of children aged 3-6 years and over 6 years, and less severe pneumonia cases.