Fig. 1 Flowchart describing the patient selection. All consecutive patients with COVID-19 aged ≥ 18 years who were hospitalized during the study period and recruited through the Japan COVID-19 Task Force between February 2020 and May 2021 were included. After excluding 242 patients, 1837 patients were enrolled in this study. *A critical case was de fi ned as receiving treatment in the intensive care unit, using invasive mechanical ventilation, or hospital