Multicenter Randomized Double-blind Placebo-controlled Study to Investigate Azvudine in Symptomatic Adults With COVID-19 at Increased Risk of Progressing to Severe Illness

Inclusion Criteria: * (1) An age of 18 years or over (inclusive); (2) Not more than five days since the development of COVID-19 symptoms, and positive for nucleic acid or antigen test for COVID-19 within five days before enrollment; (3) Presence of at least one symptom related to COVID-19 infection at the time of enrollment; (4) Agreement to practice effective birth control (for females of child-bearing potential); (5) Presence of at least one high risk factor for severe COVID-19 infection: * Age ≥ 60 years; * BMI\>25； * Fever (body temperature ≥ 38℃) for ≥ 3 days; * Current smokers (still being smoking within 30 days before enrollment and have used at least 100 cigarettes up to date); * Immunosuppressive diseases, including but not limited to: myelosuppression or organ transplantation or primary immunodeficiency disease; prolonged use of immunosuppressive agents (≥ 20 mg/d for at least 14 days in the case of prednisone within the last 30 days); biologic therapy (such as infliximab, etc.); use of immunomodulators (including but not limited to methotrexate, azathioprine, etc.); radiotherapy and/or chemotherapy for any malignancies within 90 days (for chest radiotherapy, this time interval should be more than 6 months); * Chronic lung disease (such as asthma requiring intervention daily, bronchiectasis, COPD, pulmonary hypertension, OSAS, interstitial lung disease, etc.); * Hypertension; ⑧ Cardiovascular diseases (previously diagnosed as myocardial infarction or stroke, TIA (transient ischemic attack), cardiac insufficiency, angina pectoris requiring nitrate therapy, CABG, post-PCI, post-carotid endarterectomy and aortic bypass surgery, etc.); ⑨ Type 1 or type 2 diabetes; ⑩ Neurodevelopmental abnormalities (such as cerebral palsy, Down's syndrome) or other genetic or metabolic syndromes and severe congenital malformations; ⑪ Active tumors (excluding localized skin cancer); ⑫ No vaccination against COVID-19 Exclusion Criteria: * (1) Known or suspected allergy to the components of Azvudine Tablets; (2) Patients diagnosed as severe or critical COVID-19 infection (Severe: 1. shortness of breath with RR ≥ 30 breaths/min; 2. oxygen saturation ≤ 93% when inhaling air at rest; 3. partial pressure of arterial oxygen (PaO2) / fraction of inspired oxygen (FiO2) ≤ 300 mmHg; 4. progressive worsening of clinical symptoms, and obvious lesion progression \> 50% on lung images within 24 to 48 hours. Critical: 1. respiratory failure, requiring mechanical ventilation; 2. shock; 3. concomitant organ failure, requiring care in ICU); (3) Patients with severe liver disease (total bilirubin \[TBIL\] ≥ 2 × upper limit of normal (ULN), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≥ 3 × ULN; (4) Patients with severe renal insufficiency (glomerular filtration rate ≤ 60 mL/min/1.73 m2) or currently on continuous renal replacement therapy, hemodialysis, and/or peritoneal dialysis; (5) Patients with malabsorption syndrome or any other condition compromising gastrointestinal absorption, or patients requiring parenteral nutrition or with difficulty in taking the investigational product orally; (6) Known HIV infection; (7) Presence of diabetic ketosis or hyperosmolar hyperglycemic state (HHS); (8) Total neutrophil count \< 750 cells/L; (9) Pregnant or lactating women or those who plan to have a child during participation in this study and within six months after the end of this study; (10) Currently participating in another clinical trial or currently using another investigational product; (11) Presence of other active infections (must be etiologically confirmed) in addition to COVID-19 infection; (12) Presence of any comorbidities requiring hospitalization and/or a surgical procedure within 7 days prior to the start of this study or a comorbidity considered life-threatening within 30 days prior to the start of this study; (13) Patients who have received or are expected to receive convalescent plasma for COVID-19; (14) Previous treatment with anti-viral agents that have been proved to be effective against COVID-19, including but not limited to Nirmatrelvir/Ritonavir or Molnupiravir (this criterion does not apply to use of glucocorticoids for reasons other than COVID-19); (15) Other conditions that make it inappropriate for the participant to take part in this trial at the investigator's discretion.