1.1 Patients
General information was collected at Beijing Ditan Hospital, Capital Medical University after discharged for 6 to 9 months. Of the 64 patients with confirmed COVID-19 who were followed up, all patients had pulmonary function tests, and 56 of them had their blood routine, liver function, blood coagulation, myocardial enzymes, new coronavirus nucleic acid, SARS-CoV-2 specific IgG and IgM antibody, chest CT examination, and collected the clinical manifestations and comorbidities of patients at the time of onset. Among them, 39 males (60.9%), 25 females (39.1%), age (49.31 ± 14.98) years old. The patients were divided into mild (mild symptoms without radiographic appearance of pneumonia, n=10), moderate (having symptoms and the radiographic evidence of pneumonia, with no requirement for supplemental oxygen, n=31), and severe group (having pneumonia, including one of the following: respiratory rate > 30 breaths/minute; severe respiratory distress; or SpO2 ≤ 93% on room air at rest, and critical cases (e.g. respiratory failure requiring mechanical ventilation, Septic shock, other organ failure occurrence or admission into the ICU), n=23) according to the WHO interim guidance[12] and the guidance from china[13].