- Recent (≤2weeks prior to randomization) confident diagnosis of COVID-19 confirmed by antigen detection and/or PCR, and/or seroconversion or any other emerging and validated diagnostic test. - In some patients, it may be impossible to get a confident laboratory confirmation of COVID-19 diagnosis after 24h of hospital admission because viral load is low and/or problems with diagnostic sensitivity. In those cases, in absence of an alternative diagnosis, and with highly suspect bilateral ground glass opacities on recent (<24h) chest-CT scan (confirmed by a radiologist and pulmonary physician as probable COVID-19), a patient can be enrolled as probable COVID-19 infected. In all cases, this needs confirmation by later seroconversion. - Presence of acute hypoxic respiratory failure defined as (either or both) saturation below 93% on minimal 2 l/min O2 PaO2/FiO2 below 350 - Admitted to specialized COVID-19 ward - Age 18-80 - Male or Female - Willing to provide informed consent

- Recent (≤2weeks prior to randomization) confident diagnosis of COVID-19 confirmed by antigen detection and/or PCR, and/or seroconversion or any other emerging and validated diagnostic test. - In some patients, it may be impossible to get a confident laboratory confirmation of COVID-19 diagnosis after 24h of hospital admission because viral load is low and/or problems with diagnostic sensitivity. In those cases, in absence of an alternative diagnosis, and with highly suspect bilateral ground glass opacities on recent (<24h) chest-CT scan (confirmed by a radiologist and pulmonary physician as probable COVID-19), a patient can be enrolled as probable COVID-19 infected. In all cases, this needs confirmation by later seroconversion. - Presence of acute hypoxic respiratory failure defined as (either or both) saturation below 93% on minimal 2 l/min O2 PaO2/FiO2 below 350 - Admitted to specialized COVID-19 ward - Age 18-80 - Male or Female - Willing to provide informed consent