Table 2.

Clinical classification of COVID-19 in children

Clinical classification	Clinical manifestations
Asymptomatic	No clinical signs and symptoms, lung imaging was normal, but SARS-CoV-2 nucleic acid test was positive, or positive serum-specific antibody which helped retrospective diagnosis of infection.
Mild	The clinical symptoms are mild, with symptoms of upper respiratory tract infections, including fever, cough, and sore throat, or symptoms of gastrointestinal symptoms such as nausea, vomiting, abdominal pain, and diarrhea, without sign of pneumonia.
Moderate	It could have typical COVID-19 manifestations. Fever and cough were common. In the initial stage, dry cough appeared mostly, followed by sputum cough. Some might have wheezing without obvious hypoxia such as shortness of breath, dry rales and/or wet rales. Chest imaging showed changes of pneumonia. Some children had no clinical signs and symptoms, but chest CT showed lung lesions, which were subclinical.
Severe	The disease usually progresses in about 1 week and has at least one of the following conditions: (1) Respiratory rate increased (RR): Children under 1 year of age, RR ≥ 70/min, above 1 year of age RR ≥ 50/min, with exclusion of the impact of fever and crying; (2) Blood oxygen saturation at rest < 92%; (3) With symptoms indicated hypoxia: assisted breathing (groaning, wing flaps, sags, etc.), cyanosis, intermittent apnea; (4) Unconsciousness: lethargy, coma, convulsions; (5) Refused to eat or had poor feeding, had signs of dehydration.
Critical	The disease progresses rapidly and have at least one of the following conditions: (1) Respiratory failure occurs and requires mechanical ventilation; (2) Shock; (3) Combined with other organ failures, requires intensive care unit.