Safety and Efficacy of SOF/VEL/VOX FDC for 12 Weeks and SOF/VEL for 12 Weeks in DAA-Experienced Adults With Chronic HCV Infection Who Have Not Received an NS5A Inhibitor

Key Inclusion Criteria:

- Willing and able to provide written informed consent

- HCV RNA ≥ 10^4 IU/mL at screening

- Chronic HCV infection (≥ 6 months)

- Treatment experienced with a direct acting antiviral medication not including a NS5A
Inhibitor for HCV

- Use of protocol specified methods of contraception

Key Exclusion Criteria:

- Current or prior history of clinically significant illness that may interfere with
participation in the study

- Screening ECG with clinically significant abnormalities

- Laboratory results outside of acceptable ranges at screening

- Pregnant or nursing female

- Chronic liver disease not caused by HCV

- Infection with hepatitis B virus (HBV) or human immunodeficiency virus (HIV)

Note: Other protocol defined Inclusion/Exclusion criteria may apply.