Evaluate the Efficacy and Safety of Azvudine in Preventing SARS-Cov-2 Infection in Household Contacts of Covid-19

Inclusion Criteria: 1. ≥18 years old at the signing of informed consent. 2. Household contacts of individual with symptomatic COVID-19. Symptomatic COVID-19 cases (index case) to be identified as those symptomatic and recently tested (rapid antigen test or RT-PCR) positive for SARS-CoV-2 and must fulfill the following criteria 1) collection of the first positive SARS-CoV-2 test sample less than 48 hours before randomization, 2) have at least one symptom attributable to COVID-19. 3. RT-PCR test negative (with nasopharyngeal \[NP\] swab samples) OR rapid antigen test negative at the time of screening and without any suspicious COVID-19 symptoms within 2 weeks before randomization. 4. Subject expects to be living in the same household with the symptomatic COVID-19 cases during the whole study period. 5. Willing and able to comply with study visits and study-related procedures/assessments. 6. Provide informed consent signed by study subject or legally acceptable representative. Exclusion Criteria: 1. Subject with a history of SARS-CoV-2 vaccinations within 6 months before randomization. 2. Subject with a history of SARS-CoV-2 infection within 6 months before randomization. 3. Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \>3×Upper Limit of Normal (ULN) ,or total bilirubin (TBIL) \>2×ULN. 4. Creatinine clearance (Ccr, calculated by Cockcroft-Gault equation)\<60 ml/min or Creatinine \>1.2×ULN. 5. With any serious infection requiring systemic anti-infective therapy within 14 days before randomization. 6. Allergic to the investigational agent or any components of the formulation. 7. Pregnant or breast-feeding women. 8. Previous administration of any antiretroviral drugs (e.g., antiretroviral drugs for HIV, HBV, or HCV) within 7 days before randomization. 9. Women of childbearing potential who are unwilling to practice highly effective contraception during the study, and for at least 6 months after the study; Sexually active men who are unwilling to use medically acceptable birth control during the study period. 10. Have other conditions not suitable for inclusion as judged by the investigator.