 People chronically infected with hepatitis C virus HCV are at increased risk of serious liver disease. As a result, they should receive the hepatitis B virus HBV vaccine, which can protect them from infection by HBV, another virus that targets the liver. However, people chronically infected with HCV do not respond to the HBV vaccine as effectively as healthy people without HCV. Chronic HCV infection is not thought to cause general problems with the immune system, and the reasons for this poor vaccine response are poorly understood. Previous work has shown that chronic HCV infection leads to production of chemical innate immune signals that can affect function of the immune system, but it is currently unknown how this might impact vaccination. 