Study to Evaluate the Safety and Antiviral Activity of Remdesivir (GS-5734™) in Participants With Moderate Coronavirus Disease (COVID-19) Compared to Standard of Care Treatment

Key Inclusion Criteria: * Willing and able to provide written informed consent prior to performing study procedures (participants ≥ 18 years of age) or assent (participants ≥ 12 and \< 18 years of age) prior to performing study procedures. For participants ≥ 12 and \< 18 years of age, a parent or legal guardian willing and able to provide written informed consent prior to performing study procedures * Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV)-2 infection confirmed by polymerase chain reaction (PCR) test ≤ 4 days before randomization * Currently hospitalized and requiring medical care for COVID-19 * Peripheral capillary oxygen saturation (SpO2) \> 94% on room air at screening * Radiographic evidence of pulmonary infiltrates Key Exclusion Criteria: * Participation in any other clinical trial of an experimental treatment for COVID-19 * Concurrent treatment or planned concurrent treatment with other agents with actual or possible direct acting antiviral activity against SARS-CoV-2 * Requiring mechanical ventilation at screening * Alanine Aminotransferase (ALT) or aspartate aminotransferase (AST) \> 5 X upper limit of normal (ULN) * Creatinine clearance \< 50 mL/min using the Cockcroft-Gault formula for participants ≥ 18 years of age {Cockcroft 1976} and Schwartz Formula for participants \< 18 years of age Note: Other protocol defined Inclusion/Exclusion criteria may apply.