Respiratory Viral Infection Patterns in Hospitalised Children before and after COVID-19 in Hong Kong

In the wake of Hong Kongs zero-COVID policy, this study comprehensively analyses the epidemiological shift in respiratory viruses among hospitalized pediatric patients. The research leverages a unique natural experiment created by the policys stringent measures, which led to a significant reduction in virus circulation from 2020 to early 2023. The study highlights two distinct periods: pre-COVID-19 and post-mask mandate. We used pediatric hospitalization records from January 2015 to December 2019 and March 2023 to February 2024 to reveal a notable rebound in respiratory viruses. The age-stratified analysis indicated a shift in virus susceptibility. The odds ratio of having a co-infection was significantly increased in hospitalized children aged <1 to 12 years old during the post-COVID-19 mask mandate. Moreover, the adenovirus infection in younger children was more prominent, while RSV expanded its prevalence to older children aged>6 years old and raised health concerns. The study underscores the potential long-term impacts of interrupted virus exposure on childrens immune development and the need for vigilant monitoring of respiratory virus trends. It calls for further research to elucidate the causal relationships between SARS-CoV-2 exposure, subsequent respiratory virus susceptibility, and the implications for paediatric health in the post-pandemic era. Highlights- Children (4.37 {+/-} 0.05 years old) hospitalized after COVID-19 and tested for respiratory viruses were significantly older than those (3.49 {+/-} 0.03 years old) before COVID-19. - The odds ratio of having a co-infection was significantly increased in hospitalized children aged <1 to 12 years old during the post-COVID-19 era. - In the post-COVID-19 era, the adenovirus infection in younger children was more prominent while RSV expanded its prevalence to older children aged>6 years old