Group	Classification	Criteria
Mild	Mild	Light clinical symptoms and no sign of pneumonia on imaging
	Moderate	Fever, respiratory tract symptoms, and other symptoms; imaging suggests pneumonia
Severe	Severe	Any of the following: (1) respiratory distress, respiration rate ≥ 30 times/min; (2) oxygen saturation ≤ 93% in the resting state; or (3) PaO2/FiO2 ≤ 300 mm Hg (1 mm Hg = 0.133 kPa)
	Critical	As in severe plus any of the following: (1) respiratory failure occurs, and mechanical ventilation is required; (2) shock occurs; or (3) complicated with other organ failure and need of intensive care unit monitoring and treatment