Definition
According to the NHC Guidelines, the severity of symptoms of COVID-19 was divided into “mild” and “severe.” “Severe” was defined as dyspnea, respiratory rate ≥ 30/min, blood oxygen saturation ≤ 93%, PaO2 / FiO2 ratio ≤ 300 mmHg, respiratory failure, septic shock, multiple organ dysfunction/failure, or admission to the Intensive Care Unit (Yu et al., 2020).