0	Hospital discharge or meets discharge criteria	Discharge criteria are defined as: 1 Normal body temperature for more than 3 days; 2 Significantly improved respiratory symptoms: no oxygen supplementation requirement, stable and normal vital signs for longer than 1 day; 3 Lung imaging shows obvious absorption and resolution of acute infiltrates; 4 Negative results of the nucleic acid test for SARS-CoV-2 two times consecutively, with at least a 1-day interval between tests.
1	Mild	Improving and/or mild clinical symptoms and no pneumonia changes in radiological imaging studies.
2	Moderate	Active symptoms like fever and respiratory tract symptoms and pulmonary infiltrates seen in imaging.
3	Severe	Meeting any of the following: 1 Respiratory distress, RR ≥30 breaths/min; 2 Pulse oximetry (SpO2) ≤ 93% on room air at rest state; 3 Arterial partial pressure of oxygen (PaO2)/oxygen concentration (FiO2) ≤ 300 mmHg
4	Critical illness	Meeting any of the following: 1 Mechanical ventilation; 2 Shock; 3 Other organ failure complications that require intensive care unit care
5	Death