Inclusion Criteria:  Adults (age 18 years or older). Diagnosed with SARS-CoV-2 infection by Polymerase Chain Reaction or rapid antigen test on upper respiratory tract (nasopharyngeal and oropharyngeal) specimens. Evidence of infiltrates on chest radiography or computerized tomography. Peripheral capillary oxygen saturation (SpO2) ≥94% and <22 breaths per minute (bpm) breathing room air. High risk of developing ARDS defined by a lactate dehydrogenase higher than 245 U/L, C-Reactive Protein higher than 100 mg/L, and absolute lymphocytes lower than 800 cells/µL. Eligible participants will meet two of the three before analytical criteria associated with severe COVID-19. Patients will provide written informed consent or who have a legally authorized representative available to do so. In these exceptional circumstances and following the recommendations of the Spanish Agency of Medicines and Medical Devices, the National Competent Authority of clinical trials, during the coronavirus crisis to avoid the risk of contagion, consent will be possible to obtained orally in the presence of at least one impartial witness.  Exclusion Criteria:  Patients with a history of allergy to dexamethasone. Pregnant or lactating women. Oral or inhaled corticosteroids treatment within 15 days before randomization. Immunosuppressive agent or cytotoxic drug therapy within 30 days before randomization. Neutropenia <1000 cells/µL. Human immunodeficiency virus infection with CD4 cell counts <500 cells within 90 days after randomization. Dementia. Chronic liver disease defined by ALT or AST ≥5 times the upper limit of normal. Chronic kidney injury defined by a glomerular filtration rate ≤30 ml/min, hemodialysis or peritoneal dialysis. Uncontrolled infection. Patients who are already enrolled in another clinical trial.