GS-US-540-5773

To evaluate the efficacy of 2 remdesivir (RDV) regimens with respect to  clinical status assessed by a 7-point ordinal scale on Day 14

To evaluate the safety and tolerability of RDV

1. Willing and able to provide written informed consent, or with a legal
   
   representative who can provide informed consent, or enrolled under ICH
   
   E6(R2) 4.8.15 emergency use provisions as deemed necessary by the
   
   investigator (participants ≥ 18 years of age), or willing and able to
   
   provide assent (participants ≥ 12 and < 18 years of age, where locally
   
   and nationally approved) 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
2. Aged ≥ 18 years (at all sites), or aged ≥ 12 and < 18 years of age  weighing ≥ 40 kg (where permitted according to local law and approved nationally and by the relevant institutional review board [IRB] or independent ethics committee [IEC])
3. SARS-CoV-2 infection confirmed by PCR ≤ 4 days before  randomization
4. Currently hospitalized
5. SpO2 > 94% on room air or requiring supplemental oxygen at  screening
6. Radiographc evidence of pulmonary infiltrates
7. Men and women of childbearing potential who engage in heterosexual intercourse must agree to use protocol specified method(s) of contraception as described in Protocol Appendix 3.

1. Participation in any other clinical trial of an experimental treatment for COVID-19
2. Concurrent treatment with other agents with actual or possible direct acting antiviral activity against SARS-CoV-2 is prohibited < 24 hours prior to study drug dosing
3. Evidence of multiorgan failure
4. Mechanically ventilated (including V-V ECMO) ≥ 5 days, or any duration of V-A ECMO.
5. ALT or AST > 5 x upper limit of normal (ULN)
6. 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
7. Positive pregnancy test (Protocol; Appendix 3)
8. Breastfeeding woman
9. Known hypersensitivity to the study drug, the metabolites, or formulation excipient

Part A: Remdesivir (RDV), 5 Days (Not Mechanically Ventilated)

Participants who are not mechanically ventilated will receive continued standard of care therapy together with RDV 200 mg on Day 1 followed by RDV 100 mg on Days 2, 3, 4, and 5.

Part A: Remdesivir, 10 Days (Not Mechanically Ventilated)

Participants who are not mechanically ventilated will receive continued standard of care therapy together with RDV 200 mg on Day 1 followed by RDV 100 mg on Days 2, 3, 4, 5, 6, 7, 8, 9, and 10.

Part B: Remdesivir, 5 or 10 Days (Extension)

Part B (Extension) will enroll participants after enrollment to Part A is complete. Participants will receive continued standard of care therapy together with RDV 200 mg on Day 1 followed by RDV 100 mg on Days 2-10.

Part B: Remdesivir 10 days (Mechanically Ventilated)

Participants on mechanical ventilation will receive continued standard of care therapy together with RDV 200 mg on Day 1 followed by RDV 100 mg on Days 2-10