inclusion criteria: * hospitalized * has laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (sars-cov-2) infection as determined by real time-polymerase chain reaction (pcr) at any time before randomization * evidence of infiltrates by chest x-ray, chest computed tomography (ct), lung ultrasound, or chest auscultation (rales, crackles) * informed consent must be obtained from the participant indicating that he or she understands the purpose of, and procedures required for, the study and is willing to participate in the study * critical covid-19 disease, defined as: requires supplemental oxygen delivered by nonrebreather mask or high-flow nasal cannula or use of non-invasive or invasive ventilation or requiring treatment in an intensive care unit 1. and corresponding to category 4 on the 6-point ordinal recovery scale, that is: requires one of the above modalities to sustain a peripheral capillary oxygen saturation (spo2) greater than (\>) 93 percent (%) with a fraction of inspired oxygen (fio2) of 50% or higher. note, the use of other devices may fit with category 4 if the fio2 is 50% or higher. 2. or, corresponding to category 5 on the 6-point ordinal recovery scale, that is partial pressure of oxygen in arterial per percentage of inspired oxygen (pao2/fio2) ratio \< 300 millimeter of mercury (mmhg) while on invasive mechanical ventilation or veno-venous extracorporeal membrane oxygenation (ecmo) for less than 48 hours prior to screening

inclusion criteria: * hospitalized * has laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (sars-cov-2) infection as determined by real time-polymerase chain reaction (pcr) at any time before randomization * evidence of infiltrates by chest x-ray, chest computed tomography (ct), lung ultrasound, or chest auscultation (rales, crackles) * informed consent must be obtained from the participant indicating that he or she understands the purpose of, and procedures required for, the study and is willing to participate in the study * critical covid-19 disease, defined as: requires supplemental oxygen delivered by nonrebreather mask or high-flow nasal cannula or use of non-invasive or invasive ventilation or requiring treatment in an intensive care unit 1. and corresponding to category 4 on the 6-point ordinal recovery scale, that is: requires one of the above modalities to sustain a peripheral capillary oxygen saturation (spo2) greater than (\>) 93 percent (%) with a fraction of inspired oxygen (fio2) of 50% or higher. note, the use of other devices may fit with category 4 if the fio2 is 50% or higher. 2. or, corresponding to category 5 on the 6-point ordinal recovery scale, that is partial pressure of oxygen in arterial per percentage of inspired oxygen (pao2/fio2) ratio \< 300 millimeter of mercury (mmhg) while on invasive mechanical ventilation or veno-venous extracorporeal membrane oxygenation (ecmo) for less than 48 hours prior to screening

inclusion criteria: hospitalized has laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (sars-cov-2) infection as determined by real time-polymerase chain reaction (pcr) at any time before randomization evidence of infiltrates by chest x-ray, chest computed tomography (ct), lung ultrasound, or chest auscultation (rales, crackles) informed consent must be obtained from the participant indicating that he or she understands the purpose of, and procedures required for, the study and is willing to participate in the study critical covid-19 disease, defined as: requires supplemental oxygen delivered by nonrebreather mask or high-flow nasal cannula or use of non-invasive or invasive ventilation or requiring treatment in an intensive care unit and corresponding to category 4 on the 6-point ordinal recovery scale, that is: requires one of the above modalities to sustain a peripheral capillary oxygen saturation (spo2) greater than (>) 93 percent (%) with a fraction of inspired oxygen (fio2) of 50% or higher. note, the use of other devices may fit with category 4 if the fio2 is 50% or higher. or, corresponding to category 5 on the 6-point ordinal recovery scale, that is partial pressure of oxygen in arterial per percentage of inspired oxygen (pao2/fio2) ratio < 300 millimeter of mercury (mmhg) while on invasive mechanical ventilation or veno-venous extracorporeal membrane oxygenation (ecmo) for less than 48 hours prior to screening

inclusion criteria: hospitalized has laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (sars-cov-2) infection as determined by real time-polymerase chain reaction (pcr) at any time before randomization evidence of infiltrates by chest x-ray, chest computed tomography (ct), lung ultrasound, or chest auscultation (rales, crackles) informed consent must be obtained from the participant indicating that he or she understands the purpose of, and procedures required for, the study and is willing to participate in the study critical covid-19 disease, defined as: requires supplemental oxygen delivered by nonrebreather mask or high-flow nasal cannula or use of non-invasive or invasive ventilation or requiring treatment in an intensive care unit and corresponding to category 4 on the 6-point ordinal recovery scale, that is: requires one of the above modalities to sustain a peripheral capillary oxygen saturation (spo2) greater than (>) 93 percent (%) with a fraction of inspired oxygen (fio2) of 50% or higher. note, the use of other devices may fit with category 4 if the fio2 is 50% or higher. or, corresponding to category 5 on the 6-point ordinal recovery scale, that is partial pressure of oxygen in arterial per percentage of inspired oxygen (pao2/fio2) ratio < 300 millimeter of mercury (mmhg) while on invasive mechanical ventilation or veno-venous extracorporeal membrane oxygenation (ecmo) for less than 48 hours prior to screening

inclusion criteria: - hospitalized - has laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (sars-cov-2) infection as determined by real time-polymerase chain reaction (pcr) at any time before randomization - evidence of infiltrates by chest x-ray, chest computed tomography (ct), lung ultrasound, or chest auscultation (rales, crackles) - informed consent must be obtained from the participant indicating that he or she understands the purpose of, and procedures required for, the study and is willing to participate in the study - critical covid-19 disease, defined as: requires supplemental oxygen delivered by nonrebreather mask or high-flow nasal cannula or use of non-invasive or invasive ventilation or requiring treatment in an intensive care unit 1. and corresponding to category 4 on the 6-point ordinal recovery scale, that is: requires one of the above modalities to sustain a peripheral capillary oxygen saturation (spo2) greater than (>) 93 percent (%) with a fraction of inspired oxygen (fio2) of 50% or higher. note, the use of other devices may fit with category 4 if the fio2 is 50% or higher. 2. or, corresponding to category 5 on the 6-point ordinal recovery scale, that is partial pressure of oxygen in arterial per percentage of inspired oxygen (pao2/fio2) ratio < 300 millimeter of mercury (mmhg) while on invasive mechanical ventilation or veno-venous extracorporeal membrane oxygenation (ecmo) for less than 48 hours prior to screening

inclusion criteria: - hospitalized - has laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (sars-cov-2) infection as determined by real time-polymerase chain reaction (pcr) at any time before randomization - evidence of infiltrates by chest x-ray, chest computed tomography (ct), lung ultrasound, or chest auscultation (rales, crackles) - informed consent must be obtained from the participant indicating that he or she understands the purpose of, and procedures required for, the study and is willing to participate in the study - critical covid-19 disease, defined as: requires supplemental oxygen delivered by nonrebreather mask or high-flow nasal cannula or use of non-invasive or invasive ventilation or requiring treatment in an intensive care unit 1. and corresponding to category 4 on the 6-point ordinal recovery scale, that is: requires one of the above modalities to sustain a peripheral capillary oxygen saturation (spo2) greater than (>) 93 percent (%) with a fraction of inspired oxygen (fio2) of 50% or higher. note, the use of other devices may fit with category 4 if the fio2 is 50% or higher. 2. or, corresponding to category 5 on the 6-point ordinal recovery scale, that is partial pressure of oxygen in arterial per percentage of inspired oxygen (pao2/fio2) ratio < 300 millimeter of mercury (mmhg) while on invasive mechanical ventilation or veno-venous extracorporeal membrane oxygenation (ecmo) for less than 48 hours prior to screening

inclusion criteria: hospitalized has laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (sars-cov-2) infection as determined by real time-polymerase chain reaction (pcr) at any time before randomization evidence of infiltrates by chest x-ray, chest computed tomography (ct), lung ultrasound, or chest auscultation (rales, crackles) informed consent must be obtained from the participant indicating that he or she understands the purpose of, and procedures required for, the study and is willing to participate in the study critical covid-19 disease, defined as: requires supplemental oxygen delivered by nonrebreather mask or high-flow nasal cannula or use of non-invasive or invasive ventilation or requiring treatment in an intensive care unit and corresponding to category 4 on the 6-point ordinal recovery scale, that is: requires one of the above modalities to sustain a peripheral capillary oxygen saturation (spo2) greater than (>) 93 percent (%) with a fraction of inspired oxygen (fio2) of 50% or higher. note, the use of other devices may fit with category 4 if the fio2 is 50% or higher. or, corresponding to category 5 on the 6-point ordinal recovery scale, that is partial pressure of oxygen in arterial per percentage of inspired oxygen (pao2/fio2) ratio < 300 millimeter of mercury (mmhg) while on invasive mechanical ventilation or veno-venous extracorporeal membrane oxygenation (ecmo) for less than 48 hours prior to screening

inclusion criteria: hospitalized has laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (sars-cov-2) infection as determined by real time-polymerase chain reaction (pcr) at any time before randomization evidence of infiltrates by chest x-ray, chest computed tomography (ct), lung ultrasound, or chest auscultation (rales, crackles) informed consent must be obtained from the participant indicating that he or she understands the purpose of, and procedures required for, the study and is willing to participate in the study critical covid-19 disease, defined as: requires supplemental oxygen delivered by nonrebreather mask or high-flow nasal cannula or use of non-invasive or invasive ventilation or requiring treatment in an intensive care unit and corresponding to category 4 on the 6-point ordinal recovery scale, that is: requires one of the above modalities to sustain a peripheral capillary oxygen saturation (spo2) greater than (>) 93 percent (%) with a fraction of inspired oxygen (fio2) of 50% or higher. note, the use of other devices may fit with category 4 if the fio2 is 50% or higher. or, corresponding to category 5 on the 6-point ordinal recovery scale, that is partial pressure of oxygen in arterial per percentage of inspired oxygen (pao2/fio2) ratio < 300 millimeter of mercury (mmhg) while on invasive mechanical ventilation or veno-venous extracorporeal membrane oxygenation (ecmo) for less than 48 hours prior to screening

inclusion criteria: - hospitalized - has laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (sars-cov-2) infection as determined by real time-polymerase chain reaction (pcr) at any time before randomization - evidence of infiltrates by chest x-ray, chest computed tomography (ct), lung ultrasound, or chest auscultation (rales, crackles) - informed consent must be obtained from the participant indicating that he or she understands the purpose of, and procedures required for, the study and is willing to participate in the study - critical covid-19 disease, defined as: requires supplemental oxygen delivered by nonrebreather mask or high-flow nasal cannula or use of non-invasive or invasive ventilation or requiring treatment in an intensive care unit 1. and corresponding to category 4 on the 6-point ordinal recovery scale, that is: requires one of the above modalities to sustain a peripheral capillary oxygen saturation (spo2) greater than (>) 93 percent (%) with a fraction of inspired oxygen (fio2) of 50% or higher. note, the use of other devices may fit with category 4 if the fio2 is 50% or higher. 2. or, corresponding to category 5 on the 6-point ordinal recovery scale, that is partial pressure of oxygen in arterial per percentage of inspired oxygen (pao2/fio2) ratio < 300 millimeter of mercury (mmhg) while on invasive mechanical ventilation or veno-venous extracorporeal membrane oxygenation (ecmo) for less than 48 hours prior to screening

inclusion criteria: - hospitalized - has laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (sars-cov-2) infection as determined by real time-polymerase chain reaction (pcr) at any time before randomization - evidence of infiltrates by chest x-ray, chest computed tomography (ct), lung ultrasound, or chest auscultation (rales, crackles) - informed consent must be obtained from the participant indicating that he or she understands the purpose of, and procedures required for, the study and is willing to participate in the study - critical covid-19 disease, defined as: requires supplemental oxygen delivered by nonrebreather mask or high-flow nasal cannula or use of non-invasive or invasive ventilation or requiring treatment in an intensive care unit 1. and corresponding to category 4 on the 6-point ordinal recovery scale, that is: requires one of the above modalities to sustain a peripheral capillary oxygen saturation (spo2) greater than (>) 93 percent (%) with a fraction of inspired oxygen (fio2) of 50% or higher. note, the use of other devices may fit with category 4 if the fio2 is 50% or higher. 2. or, corresponding to category 5 on the 6-point ordinal recovery scale, that is partial pressure of oxygen in arterial per percentage of inspired oxygen (pao2/fio2) ratio < 300 millimeter of mercury (mmhg) while on invasive mechanical ventilation or veno-venous extracorporeal membrane oxygenation (ecmo) for less than 48 hours prior to screening

inclusion criteria: - hospitalized - has laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (sars-cov-2) infection as determined by real time-polymerase chain reaction (pcr) at any time before randomization - evidence of infiltrates by chest x-ray, chest computed tomography (ct), lung ultrasound, or chest auscultation (rales, crackles) - informed consent must be obtained from the participant indicating that he or she understands the purpose of, and procedures required for, the study and is willing to participate in the study - severe or critical covid-19 disease: severe disease: requires supplemental oxygen administration by nasal cannula, simple face mask, or other similar oxygen delivery device. critical disease: requires supplemental oxygen delivered by nonrebreather mask or high-flow nasal cannula or use of non-invasive or invasive ventilation or requiring treatment in an intensive care unit. and at least one of the following: not receiving supplemental oxygen and having a peripheral capillary oxygen saturation (spo2) of <=93% sustained for 5 minutes (corresponds to category 3 on the 6-point ordinal scale) or receiving supplemental oxygen to sustain a peripheral capillary oxygen saturation (spo2) greater than (>) 93 percent (%) regardless of device/route used, or partial pressure of oxygen in arterial per percentage of inspired oxygen (pao2/fio2) ratio < 300 millimeter of mercury (mmhg) while on invasive mechanical ventilation or veno-venous ecmo for less than 48 hours prior to screening) (corresponds to category 5 on the 6-point ordinal scale)

inclusion criteria: - hospitalized - has laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (sars-cov-2) infection as determined by real time-polymerase chain reaction (pcr) at any time before randomization - evidence of infiltrates by chest x-ray, chest computed tomography (ct), lung ultrasound, or chest auscultation (rales, crackles) - informed consent must be obtained from the participant indicating that he or she understands the purpose of, and procedures required for, the study and is willing to participate in the study - severe or critical covid-19 disease: severe disease: requires supplemental oxygen administration by nasal cannula, simple face mask, or other similar oxygen delivery device. critical disease: requires supplemental oxygen delivered by nonrebreather mask or high-flow nasal cannula or use of non-invasive or invasive ventilation or requiring treatment in an intensive care unit. and at least one of the following: not receiving supplemental oxygen and having a peripheral capillary oxygen saturation (spo2) of <=93% sustained for 5 minutes (corresponds to category 3 on the 6-point ordinal scale) or receiving supplemental oxygen to sustain a peripheral capillary oxygen saturation (spo2) greater than (>) 93 percent (%) regardless of device/route used, or partial pressure of oxygen in arterial per percentage of inspired oxygen (pao2/fio2) ratio < 300 millimeter of mercury (mmhg) while on invasive mechanical ventilation or veno-venous ecmo for less than 48 hours prior to screening) (corresponds to category 5 on the 6-point ordinal scale)