Efficacy and Safety of Grazoprevir (+) Uprifosbuvir (+) Ruzasvir (MK-3682B) (MK-5172 + MK-3682 + MK-8408) Fixed Dose Combination in Chronic HCV Participants Failing Prior Antiviral Treatment (MK-3682-021)

Inclusion Criteria: Part A * Has documented chronic HCV GT1 or HCV GT3 infection with no evidence of non-typeable or mixed genotype. * Has documented relapse, defined as having HCV RNA target not detected at end-of-treatment, but HCV RNA quantifiable during follow-up, after treatment with one of the following DAA regimens either by approved dosage and duration or by completion of a clinical trial: GT1: SOF/LDV ± RBV; GT1: GZR/EBR ± RBV; GT3: SOF + RBV; GT3: SOF + PR; GT3: SOF + DCV ± RBV; GT3: SOF/LDV ± RBV. * Is otherwise healthy. * If male, be not of reproductive potential or agree to avoid impregnating a partner beginning at least 2 weeks prior to administration of the initial dose of study drug, through 6 months after taking the last dose of study drug (or longer if dictated by local regulations), by complying with one of the following: (1) practice abstinence from heterosexual activity or (2) use (or have their partner use) two forms of acceptable contraception during heterosexual activity which may include oral contraceptives. Part B * Has documented chronic HCV GT1, GT2, GT3, GT4, GT5, GT6 infection with no evidence of non-typeable or mixed genotype. * Has documented virologic failure, defined as having quantifiable HCV RNA at any time after completion of HCV therapy with a DAA regimen either by approved dosage and duration or by completion of a clinical trial that was not attributed to re-infection: GT1, GT2, GT4, GT5, or GT6: any prior all-oral DAA regimens; GT3: any prior all-oral DAA regimen or SOF/PR. Participants \[Parts A and B\] who previously failed PR treatment, with or without simepravir (SIM), boceprevir (BOC), or telaprevir (TPV), prior to receiving DAA therapy, may also be enrolled. Parts A and B * Has HCV RNA ≥ 10,000 IU/mL in peripheral blood at enrollment. * Has either absence of cirrhosis or presence of compensated cirrhosis. * If female, be not of reproductive potential or agree to avoid becoming pregnant beginning at least 2 weeks prior to administration of the initial dose of study drug, through either 6 months \[Part A\] or 14 days \[Part B\] after taking the last dose of study drug (or longer if dictated by local regulations), by complying with one of the following: (1) practice abstinence from heterosexual activity or (2) use (or have their partner use) two forms of acceptable contraception during heterosexual activity which may include oral contraceptives. * For HIV co-infected participants: 1) have documented HIV-1 infection \[Part A\] or HIV infection \[Part B\]; 2) either not be currently on antiretroviral therapy (ART) with no plans to initiate ART while participating in this study or have well controlled HIV on ART; and 3) have at least one viable antiretroviral regimen alternative beyond their current regimen in the event of HIV virologic failure and the development of anti-retroviral drug resistance \[Part A\]. Exclusion Criteria: Part A * Has previously received a DAA containing regimen other than the permitted regimens listed above. * Did not complete their prior DAA therapy due to intolerance to the DAA regimen or who failed the DAA regimen for reasons other than relapse (e.g., virologic breakthrough, rebound or non-response, non-compliance, lost to follow-up, withdrew consent). * Is a male whose female partner(s) is/are pregnant or is a male who is expecting to donate sperm or planning to impregnate female partner(s) from at least two weeks prior to Day 1 through at least 6 months after last dose of study drug, or longer if dictated by local regulations. * Has personal or family history of Torsade de pointes. * Has chronic pulmonary disease. * Has an hemoglobinopathy. * Has central nervous system (CNS) trauma requiring intubation, intracranial pressure monitoring, brain meningeal or skull surgery, or resulting in seizure, coma, permanent neurologic deficits, abnormal brain imaging, or cerebral spinal fluid (CSF) leak; prior brain hemorrhage and/or intracranial aneurysms (whether adequately repaired or not). * Has current or history of seizure disorder unless seizure was \>10 years ago, a single isolated event, no history of or current use of anti-seizure medications, and a documented normal neurological examination at Day 1. * Has history of stroke or transient ischemic attack. Part B * Did not complete their prior DAA therapy due to intolerance to the DAA regimen or who failed the DAA regimen for reasons other than virologic failure. * Has any major medical condition, clinically-significant illness (other than HCV), pretrial laboratory or ECG abnormality, or history of any illness that might interfere with treatment, assessment, compliance or pose additional risk in administering study drug to the participant. Parts A and B * Is under the age of legal consent, is mentally or legally incapacitated, has significant emotional problems at the time of pre-study screening visit or expected during the conduct of the study or has a history of a clinically significant psychiatric disorder which, in the opinion of the investigator, would interfere with the study procedures. * Has evidence of decompensated liver disease manifested by the presence of or history of ascites, esophageal or gastric variceal bleeding, hepatic encephalopathy or other signs or symptoms of advanced liver disease. * Has cirrhosis classified as Child-Pugh Class B or C or has a Pugh-Turcotte score \>6 * Is co-infected with hepatitis B virus (HBV) * For participants with HIV, has a history of opportunistic infection in the 6 months prior to screening. * Has a history of malignancy ≤5 years prior to enrollment except for adequately treated basal cell or squamous cell skin cancer or in situ cervical cancer or carcinoma in situ; or is under evaluation for other active or suspected malignancy. * Has cirrhosis and liver imaging within 6 months of Day 1 showing evidence of hepatocellular carcinoma (HCC) or is under evaluation for HCC. * Is currently participating or has participated in a study with an investigational compound within 30 days of signing informed consent and is not willing to refrain from participating in another such study during the course of this study (trial treatment period). Participants participating in MK-5172-017 (NCT01667081) may be enrolled in this study, MK- 3682-021. * Has clinically-relevant drug or alcohol abuse within 12 months of screening * Is a female and is pregnant or breastfeeding or expecting to conceive or donate eggs from at least 2 weeks prior to Day 1 through at least 6 months \[Part A\] or 14 days \[Part B\] after last dose of study drug, or longer if dictated by local regulations. * Has organ transplants (including hematopoietic stem cell transplants) other than cornea and hair. * Has history of gastric surgery or history of malabsorption disorders. * Has current or history of any clinically significant cardiac abnormalities/dysfunction. * Has medical/surgical conditions that may result in a need for hospitalization during the period of the study. * Has a medical condition requiring, or likely to require, chronic systemic administration of corticosteroids, tumor necrosis factor (TNF) antagonists, or other immunosuppressant drugs during the course of the study * Has evidence of history of chronic hepatitis not caused by HCV. Participants with history of acute non-HCV-related hepatitis, that resolved \>6 months before study entry, may be enrolled.