key inclusion criteria: * laboratory-confirmed sars-cov-2 infection as determined by polymerase chain reaction (pcr), result from any specimen (or other commercial or public health assay) within 2 weeks prior to randomization and no alternative explanation for current clinical condition * hospitalized with illness of any duration with evidence of pneumonia, requires supplemental oxygen and/or assisted ventilation and meets one of the following: * phase 2 and phase 3 cohort 1: meets 1 of the following criteria at baseline: * severe disease or * critical disease or * multi-system organ dysfunction or * immunocompromised * phase 3 cohort 2: patients must be receiving mechanical ventilation to treat respiratory failure due to covid-19 * phase 3 cohort 3: patients must be receiving supplemental oxygen to treat hypoxemia delivered by one of the following devices: * non-rebreather mask, or * high-flow device with at least 50% fio2, or * non-invasive positive pressure ventilator * ability to provide informed consent signed by study patient or legally acceptable representative * willingness and ability to comply with study-related procedures/assessments key

key inclusion criteria: * laboratory-confirmed sars-cov-2 infection as determined by polymerase chain reaction (pcr), result from any specimen (or other commercial or public health assay) within 2 weeks prior to randomization and no alternative explanation for current clinical condition * hospitalized with illness of any duration with evidence of pneumonia, requires supplemental oxygen and/or assisted ventilation and meets one of the following: * phase 2 and phase 3 cohort 1: meets 1 of the following criteria at baseline: * severe disease or * critical disease or * multi-system organ dysfunction or * immunocompromised * phase 3 cohort 2: patients must be receiving mechanical ventilation to treat respiratory failure due to covid-19 * phase 3 cohort 3: patients must be receiving supplemental oxygen to treat hypoxemia delivered by one of the following devices: * non-rebreather mask, or * high-flow device with at least 50% fio2, or * non-invasive positive pressure ventilator * ability to provide informed consent signed by study patient or legally acceptable representative * willingness and ability to comply with study-related procedures/assessments key

key inclusion criteria: - laboratory-confirmed sars-cov-2 infection as determined by polymerase chain reaction (pcr), result from any specimen (or other commercial or public health assay) within 2 weeks prior to randomization and no alternative explanation for current clinical condition - hospitalized with illness of any duration with evidence of pneumonia, requires supplemental oxygen and/or assisted ventilation and meets one of the following: - phase 2 and phase 3 cohort 1: meets 1 of the following criteria at baseline: - severe disease or - critical disease or - multi-system organ dysfunction or - immunocompromised - phase 3 cohort 2: patients must be receiving mechanical ventilation to treat respiratory failure due to covid-19 - phase 3 cohort 3: patients must be receiving supplemental oxygen to treat hypoxemia delivered by one of the following devices: - non-rebreather mask, or - high-flow device with at least 50% fio2, or - non-invasive positive pressure ventilator - ability to provide informed consent signed by study patient or legally acceptable representative - willingness and ability to comply with study-related procedures/assessments key

key inclusion criteria: - laboratory-confirmed sars-cov-2 infection as determined by polymerase chain reaction (pcr), result from any specimen (or other commercial or public health assay) within 2 weeks prior to randomization and no alternative explanation for current clinical condition - hospitalized with illness of any duration with evidence of pneumonia, requires supplemental oxygen and/or assisted ventilation and meets one of the following: - phase 2 and phase 3 cohort 1: meets 1 of the following criteria at baseline: - severe disease or - critical disease or - multi-system organ dysfunction or - immunocompromised - phase 3 cohort 2: patients must be receiving mechanical ventilation to treat respiratory failure due to covid-19 - phase 3 cohort 3: patients must be receiving supplemental oxygen to treat hypoxemia delivered by one of the following devices: - non-rebreather mask, or - high-flow device with at least 50% fio2, or - non-invasive positive pressure ventilator - ability to provide informed consent signed by study patient or legally acceptable representative - willingness and ability to comply with study-related procedures/assessments key

key inclusion criteria: - laboratory-confirmed sars-cov-2 infection as determined by polymerase chain reaction (pcr), result from any specimen (or other commercial or public health assay) within 2 weeks prior to randomization and no alternative explanation for current clinical condition - hospitalized with illness of any duration with evidence of pneumonia, requires supplemental oxygen and/or assisted ventilation and meets one of the following: - phase 2 and phase 3 cohort 1: meets 1 of the following criteria at baseline: - severe disease or - critical disease or - multi-system organ dysfunction or - immunocompromised - phase 3 cohort 2: patients must be receiving mechanical ventilation to treat respiratory failure due to covid-19 - ability to provide informed consent signed by study patient or legally acceptable representative - willingness and ability to comply with study-related procedures/assessments key

key inclusion criteria: - laboratory-confirmed sars-cov-2 infection as determined by polymerase chain reaction (pcr), result from any specimen (or other commercial or public health assay) within 2 weeks prior to randomization and no alternative explanation for current clinical condition - hospitalized with illness of any duration with evidence of pneumonia, requires supplemental oxygen and/or assisted ventilation and meets one of the following: - phase 2 and phase 3 cohort 1: meets 1 of the following criteria at baseline: - severe disease or - critical disease or - multi-system organ dysfunction or - immunocompromised - phase 3 cohort 2: patients must be receiving mechanical ventilation to treat respiratory failure due to covid-19 - ability to provide informed consent signed by study patient or legally acceptable representative - willingness and ability to comply with study-related procedures/assessments key