For mild/moderate SARS-CoV-2-infected participants:- Participants who were diagnosed as SARS-CoV-2 positive within 120 hours before randomization.- Participants with time from COVID-19 onset to randomization of =< 120 hours.- Participants who have at least one moderate or severe symptom among the following 12 symptoms of COVID-19 at the time of randomization.(low energy or tiredness, muscle or body aches, headache, chills or shivering, feeling hot or feverish, stuffy or runny nose, sore throat, cough, shortness of breath, nausea, vomiting, diarrhea)For asymptomatic SARS-CoV-2-infected participants (Phase 2a Part):- Participants who were diagnosed as SARS-CoV-2 positive within 120 hours before randomizationt.- Participants who have none of the following 14 symptoms of COVID-19 within 2 weeks before randomization.(low energy or tiredness, muscle or body aches, headache, chills or shivering, feeling hot or feverish, taste disorder, smell disorder, stuffy or runny nose, sore throat, cough, shortness of breath, nausea, vomiting, diarrhea)For asymptomatic/only mild symptoms SARS-CoV-2-infected participants (Phase 2b/3 Part):- Participants who were diagnosed as SARS-CoV-2 positive within 120 hours before randomizationt.- Participants who do not have any symtoms of moderate or severe symptom among the 12 symptoms of COVID-19 at the time of randomization.

For mild/moderate SARS-CoV-2-infected participants:- Participants who were diagnosed as SARS-CoV-2 positive within 120 hours before randomization.- Participants with time from COVID-19 onset to randomization of =< 120 hours.- Participants who have at least one moderate or severe symptom among the following 12 symptoms of COVID-19 at the time of randomization.(low energy or tiredness, muscle or body aches, headache, chills or shivering, feeling hot or feverish, stuffy or runny nose, sore throat, cough, shortness of breath, nausea, vomiting, diarrhea)For asymptomatic SARS-CoV-2-infected participants (Phase 2a Part):- Participants who were diagnosed as SARS-CoV-2 positive within 120 hours before randomizationt.- Participants who have none of the following 14 symptoms of COVID-19 within 2 weeks before randomization.(low energy or tiredness, muscle or body aches, headache, chills or shivering, feeling hot or feverish, taste disorder, smell disorder, stuffy or runny nose, sore throat, cough, shortness of breath, nausea, vomiting, diarrhea)For asymptomatic/only mild symptoms SARS-CoV-2-infected participants (Phase 2b/3 Part):- Participants who were diagnosed as SARS-CoV-2 positive within 120 hours before randomizationt.- Participants who do not have any symtoms of moderate or severe symptom among the 12 symptoms of COVID-19 at the time of randomization.

Common for Phase 2a Part and Phase 2b/3 PartFor mild/moderate SARS-CoV-2-infected participants:- Participants who were diagnosed as SARS-CoV-2 positive within 120 hours before enrollment.- Participants with time from COVID-19 onset to enrollment of =< 120 hours.- Participants who have at least one moderate or severe symptom among the following 12 symptoms of COVID-19 at the time of enrollment(low energy or tiredness, muscle or body aches, headache, chills or shivering, feeling hot or feverish, stuffy or runny nose, sore throat, cough, shortness of breath, nausea, vomiting, diarrhea)For asymptomatic SARS-CoV-2-infected participants:- Participants who were diagnosed as SARS-CoV-2 positive within 120 hours before enrollment.- Participants who have none of the following 14 symptoms of COVID-19 within 2 weeks before enrollment.(low energy or tiredness, muscle or body aches, headache, chills or shivering, feeling hot or feverish, taste disorder, smell disorder, stuffy or runny nose, sore throat, cough, shortness of breath, nausea, vomiting, diarrhea)

Common for Phase 2a Part and Phase 2b/3 PartFor mild/moderate SARS-CoV-2-infected participants:- Participants who were diagnosed as SARS-CoV-2 positive within 120 hours before enrollment.- Participants with time from COVID-19 onset to enrollment of =< 120 hours.- Participants who have at least one moderate or severe symptom among the following 12 symptoms of COVID-19 at the time of enrollment(low energy or tiredness, muscle or body aches, headache, chills or shivering, feeling hot or feverish, stuffy or runny nose, sore throat, cough, shortness of breath, nausea, vomiting, diarrhea)For asymptomatic SARS-CoV-2-infected participants:- Participants who were diagnosed as SARS-CoV-2 positive within 120 hours before enrollment.- Participants who have none of the following 14 symptoms of COVID-19 within 2 weeks before enrollment.(low energy or tiredness, muscle or body aches, headache, chills or shivering, feeling hot or feverish, taste disorder, smell disorder, stuffy or runny nose, sore throat, cough, shortness of breath, nausea, vomiting, diarrhea)

Common for Phase 2a Part and Phase 2b/3 PartFor mild SARS-CoV-2-infected participants:- Participants who were diagnosed as SARS-CoV-2 positive within 120 hours before enrollment.- Participants with time from COVID-19 onset to enrollment of =< 120 hours.- Participants who have at least one moderate or severe symptom among the following 12 symptoms of COVID-19 at the time of enrollment(low energy or tiredness, muscle or body aches, headache, chills or shivering, feeling hot or feverish, stuffy or runny nose, sore throat, cough, shortness of breath, nausea, vomiting, diarrhea)For asymptomatic SARS-CoV-2-infected participants:- Participants who were diagnosed as SARS-CoV-2 positive within 120 hours before enrollment.- Participants who have none of the following 14 symptoms of COVID-19 within 2 weeks before enrollment.(low energy or tiredness, muscle or body aches, headache, chills or shivering, feeling hot or feverish, taste disorder, smell disorder, stuffy or runny nose, sore throat, cough, shortness of breath, nausea, vomiting, diarrhea)

Common for Phase 2a Part and Phase 2b/3 PartFor mild SARS-CoV-2-infected participants:- Participants who were diagnosed as SARS-CoV-2 positive within 120 hours before enrollment.- Participants with time from COVID-19 onset to enrollment of =< 120 hours.- Participants who have at least one moderate or severe symptom among the following 12 symptoms of COVID-19 at the time of enrollment(low energy or tiredness, muscle or body aches, headache, chills or shivering, feeling hot or feverish, stuffy or runny nose, sore throat, cough, shortness of breath, nausea, vomiting, diarrhea)For asymptomatic SARS-CoV-2-infected participants:- Participants who were diagnosed as SARS-CoV-2 positive within 120 hours before enrollment.- Participants who have none of the following 14 symptoms of COVID-19 within 2 weeks before enrollment.(low energy or tiredness, muscle or body aches, headache, chills or shivering, feeling hot or feverish, taste disorder, smell disorder, stuffy or runny nose, sore throat, cough, shortness of breath, nausea, vomiting, diarrhea)