This is a randomized, double-blind, placebo-controlled, phase II/III clinical study to evaluate the efficacy and safety of SSD8432 in combination with ritonavir in adult subjects with mild/common COVID-19.

This is a randomized, double-blind, placebo-controlled, phase II/III clinical study to evaluate the efficacy and safety of SSD8432 in combination with ritonavir in adult subjects with mild/common COVID-19.

This study plan to enroll 670 mild or common type adult COVID-19 subjects, Randomly assigned to the experimental group and the control group according to 1:1, experimental group:335subjects will receive SSD8432 and Ritonavir; control group :335subjects will receive SSD8432 placebo and Ritonavir placebo.

Inclusion Criteria:

1. ≥18 and ≤80 years old, male or female.
2. Initial positive test of SARS-CoV-2 within 5 days of randomization.
3. mild or common type of COVID-19.
4. Initial onset of COVID-19 signs/symptoms within 3 days of randomization.
5. Fever or 1 respiratory symptom of COVID-19 on random day
6. Subjects without high risk factors
7. Subjects with at least one high-risk factor

Exclusion Criteria:

1. Transnasal high-flow oxygen therapy or non-invasive ventilation, invasive mechanical ventilation, or ECMO is required or anticipated to be urgently required.
2. Prior to current disease episode, any confirmed SARS-CoV-2 infection.
3. Known medical history of active liver disease (other than nonalcoholic hepatic steatosis).
4. Receiving dialysis or have known moderate to severe renal impairment.
5. Known human immunodeficiency virus (HIV) infection.
6. Suspected or confirmed concurrent active systemic infection other than COVID-19 that may interfere with the evaluation of response to the study intervention.
7. Oxygen saturation of ≤ 93% on room air obtained at rest within 24 hours prior to randomization..
8. Treatment with antivirals against SARS-CoV-2 within 14 days.
9. Current or expected use of any medications or substances that are highly dependent on CYP3A4 for clearance.
10. Concomitant use of any medications or substances that are strong inducers of CYP3A4 are prohibited within 28 days.
11. Has received or is expected to receive COVID-19 monoclonal antibody, convalescent COVID-19 plasma or other prohibited concomitant medication.
12. Females who are pregnant or breastfeeding.