* participants who are judged by the investigator as likely to progress to severe/critical covid-19 prior to randomization. * participants who have spo2≤93% on room air at sea level or pao2/fio2≤ 300, or respiratory rate ≥30 per minute. * participants who require mechanical ventilation or anticipated impending need for mechanical ventilation. * participants who have eye disease. * participants who have any of the following conditions when screening: alt or ast\>1.5 uln; e gfr \<60 ml/min. * participants who have known allergies to any of the components used in the formulation of the interventions. * any medical condition, which in the opinion of the investigator, will compromise the safety of the participant. * participants who have received a sars-cov-2 monoclonal antibody treatment or prevention, or antiviral treatment (including the investigational treatment). * participants who have received convalescent covid-19 plasma treatment. * participant's use of contraindicated drugs in the package insert of nirmatrelvir tablet/ritonavir tablets. * participants who have participated, within the last 30 days, in a clinical study involving an investigational intervention. if the previous investigational intervention has a long half-life, 5 half-lives or 30 days, whichever is longer, should have passed. * participants who are concurrently enrolled in any other type of medical research judged not to be scientifically or medically compatible with this study. * female who is pregnant or breast-feeding or plan to be pregnant within this study period. * male whose wife or partner plan to be pregnant within this study period.

* participants who are judged by the investigator as likely to progress to severe/critical covid-19 prior to randomization. * participants who have spo2≤93% on room air at sea level or pao2/fio2≤ 300, or respiratory rate ≥30 per minute. * participants who require mechanical ventilation or anticipated impending need for mechanical ventilation. * participants who have eye disease. * participants who have any of the following conditions when screening: alt or ast\>1.5 uln; e gfr \<60 ml/min. * participants who have known allergies to any of the components used in the formulation of the interventions. * any medical condition, which in the opinion of the investigator, will compromise the safety of the participant. * participants who have received a sars-cov-2 monoclonal antibody treatment or prevention, or antiviral treatment (including the investigational treatment). * participants who have received convalescent covid-19 plasma treatment. * participant's use of contraindicated drugs in the package insert of nirmatrelvir tablet/ritonavir tablets. * participants who have participated, within the last 30 days, in a clinical study involving an investigational intervention. if the previous investigational intervention has a long half-life, 5 half-lives or 30 days, whichever is longer, should have passed. * participants who are concurrently enrolled in any other type of medical research judged not to be scientifically or medically compatible with this study. * female who is pregnant or breast-feeding or plan to be pregnant within this study period. * male whose wife or partner plan to be pregnant within this study period.

participants who are judged by the investigator as likely to progress to severe/critical covid-19 prior to randomization. participants who have spo2≤93% on room air at sea level or pao2/fio2≤ 300, or respiratory rate ≥30 per minute. participants who require mechanical ventilation or anticipated impending need for mechanical ventilation. participants who have eye disease. participants who have any of the following conditions when screening: alt or ast>1.5 uln; e gfr <60 ml/min. participants who have known allergies to any of the components used in the formulation of the interventions. any medical condition, which in the opinion of the investigator, will compromise the safety of the participant. participants who have received a sars-cov-2 monoclonal antibody treatment or prevention, or antiviral treatment (including the investigational treatment). participants who have received convalescent covid-19 plasma treatment. participant's use of contraindicated drugs in the package insert of nirmatrelvir tablet/ritonavir tablets. participants who have participated, within the last 30 days, in a clinical study involving an investigational intervention. if the previous investigational intervention has a long half-life, 5 half-lives or 30 days, whichever is longer, should have passed. participants who are concurrently enrolled in any other type of medical research judged not to be scientifically or medically compatible with this study. female who is pregnant or breast-feeding or plan to be pregnant within this study period. male whose wife or partner plan to be pregnant within this study period.

participants who are judged by the investigator as likely to progress to severe/critical covid-19 prior to randomization. participants who have spo2≤93% on room air at sea level or pao2/fio2≤ 300, or respiratory rate ≥30 per minute. participants who require mechanical ventilation or anticipated impending need for mechanical ventilation. participants who have eye disease. participants who have any of the following conditions when screening: alt or ast>1.5 uln; e gfr <60 ml/min. participants who have known allergies to any of the components used in the formulation of the interventions. any medical condition, which in the opinion of the investigator, will compromise the safety of the participant. participants who have received a sars-cov-2 monoclonal antibody treatment or prevention, or antiviral treatment (including the investigational treatment). participants who have received convalescent covid-19 plasma treatment. participant's use of contraindicated drugs in the package insert of nirmatrelvir tablet/ritonavir tablets. participants who have participated, within the last 30 days, in a clinical study involving an investigational intervention. if the previous investigational intervention has a long half-life, 5 half-lives or 30 days, whichever is longer, should have passed. participants who are concurrently enrolled in any other type of medical research judged not to be scientifically or medically compatible with this study. female who is pregnant or breast-feeding or plan to be pregnant within this study period. male whose wife or partner plan to be pregnant within this study period.