Respiratory syncytial virus and influenza epidemics disappearance in Korea during the 2020-2021 season of COVID-19.

Abstract Objectives We investigated whether non-pharmaceutical interventions (NPIs) reduce winter-prevalent respiratory viral infections represented by a respiratory syncytial virus (RSV) and influenza virus (IFV) during the winter in Korea. Methods The Korean Influenza and Respiratory Virus Monitoring System database was used. From January 2016 through January 2021, the weekly positivity of respiratory viruses and the weekly number of hospitalizations with acute respiratory infections were collected. The NPI period was defined as February 2020–January 2021. We analyzed whether hospitalization and sample positivity by respiratory viruses changed after NPIs. Bayesian structural time–series models and Poisson analyses were used. Data from other countries/regions reporting positive rates of RSV and IFV were also investigated. Results Compared with the pre-NPI period, the positive rates of RSV and IFV decreased significantly to 19% and 6%, and 23% and 6% of the predicted value. Also, hospitalization significantly decreased to 9% and 8%, and 10% and 5% of the predicted value. The positive rates of IFV in 14 countries during the NPI period were almost 0, whereas sporadic outbreaks of RSV occurred in some countries. Conclusions No RSV and IFV winter epidemics were observed during the 2020–2021 season in Korea.