['hepatitis c virus infection']
['sof/vel', 'placebo']

        Inclusion Criteria:

          -  Willing and able to provide written informed consent

          -  HCV RNA ≥ 10^4 IU/mL at screening

          -  HCV genotype 1, 2, 4, 5, 6, or indeterminate assessed at screening by the central
             laboratory

          -  Chronic HCV infection (≥ 6 months) documented by prior medical history or liver biopsy

          -  Classification as treatment naive or treatment experienced

          -  Males and females of childbearing potential who engage in heterosexual intercourse
             must agree to use protocol specified method(s) of contraception

        Exclusion Criteria:

          -  Current or prior history of clinically-significant illness (other than HCV) or any
             other major medical disorder that may interfere with treatment, assessment, or
             compliance with the protocol; individuals currently under evaluation for a potentially
             clinically-significant illness (other than HCV) are also excluded.

          -  Screening ECG with clinically significant abnormalities

          -  Laboratory results outside of acceptable ranges at Screening

          -  Prior exposure to SOF or other nucleotide analogue HCV NS5B inhibitor or any HCV NS5A
             inhibitor

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