Comparison of the incidence of severe outcomes in outpatients with COVID-19 or seasonal influenza without risk factors: Retrospective analysis of a health insurance claims-database

Background: To evaluate disease severity for coronavirus disease of 2019 (COVID-19), seasonal influenza (FLU) is often used as a control group for comparison. However, evidence regarding outpatients without risk factors for severe disease is insufficient to consider future treatment policies for these patients. Objectives: To compare the risk of severe disease in patients without risk factors for severe disease who are diagnosed with COVID-19 or FLU. Study design: This was a retrospective study analyzing a health insurance claims database (data collection: COVID-19, January 2020 through August 2022; FLU, October 2017 through September 2019). Outcome measures were incidences of severe events of hospitalization, respiratory and heart rate monitoring, oxygen therapy, ventilator use, and intensive care unit admission (within 28 days from diagnosis), and death (within the following month). Results: Data from 575,293 patients were included in the COVID-19 group and from 1,095,698 patients in the FLU group, without risk factors. Adjusted odds ratios for all study outcomes were significantly higher for patients with COVID-19 than with FLU (>3 times greater odds ratio for all severe events). For the population aged ≥18 years, there was also a significantly higher risk for all severe events with COVID-19 versus FLU. The incidence of severe events with COVID-19 among the population aged