Definitions of Response

Rapid virologic response (RVR): undetectable hepatitis C virus (HCV) RNA at week 4. Extended RVR (eRVR): HCV RNA <10-15 IU/ml at weeks 4 and 12, as defined by clinical trials with telaprevir (TVR)-based therapy (12, 13) . Early virologic response (EVR): ≥ 2 log ₁₀ reduction from baseline HCV RNA, but virus remains detectable (partial EVR) or is undetectable (complete EVR) at week 12. Early responders: HCV RNA <10-15 IU/ml at week 8, as defined by clinical trials with boceprevir (BOC)-based therapy (11, 14) . Partial response: ≥ 2 log ₁₀ reduction from baseline HCV RNA at week 12, but virus remains detectable through week 24 or treatment end. Breakthrough: undetectable HCV RNA during treatment followed by appearance of HCV RNA, despite continued treatment. End-of-treatment response (ETR): undetectable HCV RNA at the end of treatment. Sustained virologic response (SVR): undetectable HCV RNA at 24 weeks after treatment completion. Relapse: undetectable viremia during treatment and/or at the end of treatment, but subsequent viremia following treatment cessation. Non-response: detectable circulating HCV RNA throughout treatment. Null-response: <2 log ₁₀ reduction from baseline HCV RNA during treatment DAA, direct-acting antiviral; PegIFN, peginterferon; RBV, ribavirin.