* signs of acute respiratory distress syndrome or respiratory failure necessitating mechanical ventilation at time of screening/randomization or anticipated need for mechanical ventilation * history of severe chronic respiratory disease and requirement for long-term oxygen therapy * uncontrolled active systemic infection or hemodynamic instability requiring admission to an intensive care unit * malignant tumor receiving treatment, or other serious systemic diseases affecting life expectancy within 29 days of screening * receipt of cancer chemotherapy or immunomodulatory drugs during preceding 2 months (steroids for treatment of covid-19 are acceptable) * convalescent plasma (ccp) or anti-sars-cov-2 monoclonal antibodies administered \<24 hours prior to randomization. must have recovered from any adverse events related to ccp treatment. received chloroquine or hydroxychloroquine within last 7 days or during the study * current participation in other clinical trials including extended access programs * active deep vein thrombosis or pulmonary embolism within last 6 months * anticipated discharge from hospital or transfer to another hospital which is not a study site within 48 hours of admission * active uncontrolled co-morbid disease that may interfere with study conduct or interpretation of findings * known to be positive for hiv or positive test for chronic hbv infection or positive test for hepatitis c antibody * pregnancy or breast feeding

* signs of acute respiratory distress syndrome or respiratory failure necessitating mechanical ventilation at time of screening/randomization or anticipated need for mechanical ventilation * history of severe chronic respiratory disease and requirement for long-term oxygen therapy * uncontrolled active systemic infection or hemodynamic instability requiring admission to an intensive care unit * malignant tumor receiving treatment, or other serious systemic diseases affecting life expectancy within 29 days of screening * receipt of cancer chemotherapy or immunomodulatory drugs during preceding 2 months (steroids for treatment of covid-19 are acceptable) * convalescent plasma (ccp) or anti-sars-cov-2 monoclonal antibodies administered \<24 hours prior to randomization. must have recovered from any adverse events related to ccp treatment. received chloroquine or hydroxychloroquine within last 7 days or during the study * current participation in other clinical trials including extended access programs * active deep vein thrombosis or pulmonary embolism within last 6 months * anticipated discharge from hospital or transfer to another hospital which is not a study site within 48 hours of admission * active uncontrolled co-morbid disease that may interfere with study conduct or interpretation of findings * known to be positive for hiv or positive test for chronic hbv infection or positive test for hepatitis c antibody * pregnancy or breast feeding

- signs of acute respiratory distress syndrome or respiratory failure necessitating mechanical ventilation at time of screening/randomization or anticipated need for mechanical ventilation - history of severe chronic respiratory disease and requirement for long-term oxygen therapy - uncontrolled active systemic infection or hemodynamic instability requiring admission to an intensive care unit - malignant tumor receiving treatment, or other serious systemic diseases affecting life expectancy within 29 days of screening - receipt of cancer chemotherapy or immunomodulatory drugs during preceding 2 months (steroids for treatment of covid-19 are acceptable) - current participation in other clinical trials including extended access programs - active deep vein thrombosis or pulmonary embolism within last 6 months - anticipated discharge from hospital or transfer to another hospital which is not a study site within 48 hours of admission - active uncontrolled co-morbid disease that may interfere with study conduct or interpretation of findings - known to be positive for hiv or positive test for chronic hbv infection or positive test for hepatitis c antibody - convalescent plasma (ccp) or anti-sars-cov-2 monoclonal antibodies administered <24 hours prior to randomization. must have recovered from any adverse events related to ccp treatment. received chloroquine or hydroxychloroquine within last 7 days or during the study - pregnancy or breast feeding

- signs of acute respiratory distress syndrome or respiratory failure necessitating mechanical ventilation at time of screening/randomization or anticipated need for mechanical ventilation - history of severe chronic respiratory disease and requirement for long-term oxygen therapy - uncontrolled active systemic infection or hemodynamic instability requiring admission to an intensive care unit - malignant tumor receiving treatment, or other serious systemic diseases affecting life expectancy within 29 days of screening - receipt of cancer chemotherapy or immunomodulatory drugs during preceding 2 months (steroids for treatment of covid-19 are acceptable) - current participation in other clinical trials including extended access programs - active deep vein thrombosis or pulmonary embolism within last 6 months - anticipated discharge from hospital or transfer to another hospital which is not a study site within 48 hours of admission - active uncontrolled co-morbid disease that may interfere with study conduct or interpretation of findings - known to be positive for hiv or positive test for chronic hbv infection or positive test for hepatitis c antibody - convalescent plasma (ccp) or anti-sars-cov-2 monoclonal antibodies administered <24 hours prior to randomization. must have recovered from any adverse events related to ccp treatment. received chloroquine or hydroxychloroquine within last 7 days or during the study - pregnancy or breast feeding