Inclusion Criteria:  Chronic hepatitis C virus (HCV) infection, defined as the presence of HCV RNA for ≥ 6 months Age ≥ 20 years Patients with any HCV genotype (genotype 1-6 or indeterminate genotype) who failed to NS5A-containing DAA regimen or patients with HCV genotype 1a or 3 who failed to non-NS5A-containing DAA regimen  Exclusion Criteria:  Decompensated cirrhosis Patients who receive concomitant medications which are contraindicated for SOF/VEL/VOX, and who decline to stop or switch contraindicated concomitant medications Patients who receive therapeutic vaccination or other investigational agents for HCV