Inclusion Criteria:  Age 18 to 90, male and female subject of any race Reverse transcriptase Polymerase Chain Reaction (rt-PCR)-confirmed COVID-19 infection based on a nasal / oropharyngeal swab within 10 days before randomization  At least one of the following: 1) Respiratory distress with tachypnea (RR ≥ 24 breaths/min without oxygen); 2) Partial arterial oxygen pressure (PaO2) / Fraction of inspiration O2 (FiO2), P/F >100 and <300 mmHg (1mmHg = 0.133kPa), 3) SpO2 ≤ 94% while breathing ambient air.  Calculation through validated Sat/FiO2 scales is allowed. P/F value of reference if the last available before the signature of consent.  Need of supplemental oxygen (i.e. new use of supplemental oxygen, or increased oxygen requirement if on chronic oxygen) requiring low- or high-flow oxygen or non-invasive mechanical ventilation (7-point WHO-OS category 4 or 5). Radiological chest imaging (X-rays, CT scan) confirms lung involvement and inflammation.  Exclusion Criteria:  Cannot obtain informed consent. Hepatic dysfunction with Child Pugh score B or C, or ALT or AST> 5 times the upper limit. Renal dysfunction with estimated glomerular filtration rate (MDRD) < 50 mL/min/1.73 m2 or patient receiving continuous renal replacement therapy, hemodialysis, or peritoneal dialysis. Bacterial sepsis (besides COVID-19 sepsis). Known congenital or acquired immune deficiency. Positive or missing pregnancy test before first drug intake or day 1; pregnant or lactating women; women of childbearing potential and fertile men who do not agree to use at least one primary form of contraception for the duration of the study.