Background: In elderly patients, respiratory virus infection is related to mortality. Social distancing during the COVID-19 pandemic has significantly reduced respiratory virus infections. However, respiratory virus infections are gradually increasing after social distancing is lifted.

Objective: To identify changes in the epidemiology of severe acute respiratory virus infection in the elderly after social distancing was lifted

Method: This study was a retrospective analysis using data collected prospectively from a nationwide severe acute respiratory infections (SARIs) surveillance database between May 2020 and December 2022 at 42 sentinel sites.

Results: The study enrolled 4,930 people during the social distancing period and 4,278 people during the lifting period. In both periods, the mean age was 77 years and 64% were male. After social distancing was lifted, the number of SARIs per 1000 hospitalized patients increased significantly from 0.0802 to 0.2093 (P<0.001). In addition, the number of SARI-related intensive care unit admissions per 1000 hospitalized patients increased from 0.0179 to 0.034 (P=0.034), and the SARI-related death rate increased from 0.0095 to 0.0326 (P<0.001). Among the respiratory viruses, respiratory syncytial virus infection and metapneumovirus infection were significantly increased.

Conclusions: After social distancing was lifted, SARIs, particularly respiratory syncytial virus infection and metapneumovirus infection, increased significantly. Therefore, active surveillance of respiratory virus and treatment are needed to reduce the mortality of elderly patients.