Early-stage Trial to Determine a Safe and Effective Dose for Ratutrelvir in Patients With Mild to Moderate COVID-19

Inclusion Criteria: 1. Confirmed SARS-CoV-2 infection for 120 h prior to randomization. 2. Initial onset of signs/symptoms attributable to COVID-19 within 5 days prior to randomization. 3. At least one of the symptoms attributable to COVID-19 present within 24 hours prior to the Day 1 with the severity score of 1 or higher according to the following scoring system for the assessment of severity of: Exclusion Criteria: Medical Conditions: 1. History, current need for hospitalization or anticipated need for hospitalization for the medical treatment of COVID-19. 2. Urgent or expected need for nasal high-flow oxygen therapy or positive pressure ventilation, invasive mechanical ventilation or ECMO. 3. Known medical history of active liver disease . 4. Receiving dialysis or history of moderate to severe renal impairment. 5. Compromised immune system. 6. Acute episode of chronic respiratory diseases, including bronchial asthma, chronic obstructive pulmonary disease within 30 days before screening. 7. Suspected or confirmed concurrent active systemic infection.. Prior/Concomitant Therapy: 8. Has received or is expected to receive any dose of a SARS-CoV-2 vaccine within 4 months of screening and during the participation in the study. 9. Concomitant use of any medications or substances that are strong inducers of CYP3A4