Hepatitis C is a disease that affects the liver and is caused by the hepatitis C virus (HCV). Approximately 3.2 million people in the United States are thought to have chronic hepatitis C. The virus replicates in the liver and triggers an immune response that can lead to liver scarring and loss of function over many years. Most people develop a chronic HCV infection, though some clear the virus early on. Hepatitis C is diagnosed through antibody and RNA tests to detect the virus. There is no vaccine and many people are unaware they are infected.