* a negative rt-pcr test for covid-19 during the evaluation of the present illness * extracorporeal membrane oxygenation (ecmo) * pregnant or lactating women * active underlying cancer treated with systemic chemotherapy or radiation therapy during the last 30 days * transplantation of hematopoietic or solid organs * chronic mechanical ventilation or dialysis * otherwise unsuitable for study participation because of chronic, severe, end-stage, and life-limiting underlying disease unrelated to covid-19 likely to interfere with management and assessment of acute pneumonia, only comfort or limited (non-aggressive) care is to be given, or life expectancy \<6 months unrelated to acute covid infection in the opinion of the investigator

* a negative rt-pcr test for covid-19 during the evaluation of the present illness * extracorporeal membrane oxygenation (ecmo) * pregnant or lactating women * active underlying cancer treated with systemic chemotherapy or radiation therapy during the last 30 days * transplantation of hematopoietic or solid organs * chronic mechanical ventilation or dialysis * otherwise unsuitable for study participation because of chronic, severe, end-stage, and life-limiting underlying disease unrelated to covid-19 likely to interfere with management and assessment of acute pneumonia, only comfort or limited (non-aggressive) care is to be given, or life expectancy \<6 months unrelated to acute covid infection in the opinion of the investigator

- a negative rt-pcr test for covid-19 during the evaluation of the present illness - extracorporeal membrane oxygenation (ecmo) - pregnant or lactating women - active underlying cancer treated with systemic chemotherapy or radiation therapy during the last 30 days - transplantation of hematopoietic or solid organs - chronic mechanical ventilation or dialysis - otherwise unsuitable for study participation because of chronic, severe, end-stage, and life-limiting underlying disease unrelated to covid-19 likely to interfere with management and assessment of acute pneumonia, only comfort or limited (non-aggressive) care is to be given, or life expectancy <6 months unrelated to acute covid infection in the opinion of the investigator

- a negative rt-pcr test for covid-19 during the evaluation of the present illness - extracorporeal membrane oxygenation (ecmo) - pregnant or lactating women - active underlying cancer treated with systemic chemotherapy or radiation therapy during the last 30 days - transplantation of hematopoietic or solid organs - chronic mechanical ventilation or dialysis - otherwise unsuitable for study participation because of chronic, severe, end-stage, and life-limiting underlying disease unrelated to covid-19 likely to interfere with management and assessment of acute pneumonia, only comfort or limited (non-aggressive) care is to be given, or life expectancy <6 months unrelated to acute covid infection in the opinion of the investigator