Reduction of influenza in Osaka, Japan during the COVID-19 outbreak: a population-based ORION registry study.

Objectives: The spread of COVID-19 has affected the incidence of other infectious diseases, but there are no reports of studies using comprehensive regional population-based data to evaluate the impact of COVID-19 on influenza incidence. We attempted to evaluate the impact of COVID-19 on influenza using the population-based ORION (Osaka Emergency Information Research Intelligent Operation Network) registry.

Methods: The ORION registry of emergency patients treated by emergency medical service (EMS) personnel was developed by the Osaka Prefecture government. From ORION, we included emergency patients with influenza using the ICD (International Statistical Classification of Diseases and Related Health Problems) 10 codes. Influenza incidence rate ratio (IRR) and associated 95% CI were calculated.

Results: The number of influenza patients transported by EMS decreased during the COVID-19 pandemic. The IRR showed a substantial decrease in influenza patients in 2020 (IRR 2020/2018 0.39, 95% CI 0.37-0.41).

Conclusions: A comprehensive regional analysis using the population-based ORION registry confirmed that from January 2020, when the first confirmed cases of COVID-19 infection were reported in Osaka, Japan, the number of influenza patients transported by EMS decreased dramatically.