Table 1.

Classification of COVID-19.

Classification	Mild	Moderate	Severe	Critical	Ref.
Signs & symptoms	Mild symptoms	Fever	Respiratory distress ≥30 breaths/min	Respiratory failure and requiring mechanical ventilation	(9)
		Respiratory symptoms	Resting SpO2 ≤ 93%	Shock
			Arterial partial pressure of oxygen (PaO2)/fraction of inspired oxygen (FiO2)≤300mmHg (l mmHg = 0.133 kPa)	With another organ failure necessitating ICU care
Imaging	No signs of pneumonia	Signs of pneumonia present	Obvious lesion progression within 24–48h >50%	Diffuse pulmonary involvement (“white lung”)	(9, 10)
Pathogenesis	Increased viral replication	Viral replication continues	Predominant inflammatory response	Inflammatory response	(11, 12)
		Inflammatory response	Reduced viral replication
Therapeutic Intervention	Antiviral drugs	Antiviral drugs	Anti-inflammatory drugs	Anti-inflammatory drugs	(11, 12)
	Antibody therapy	Antibody therapy	Antiviral drugs