HBV is a contagious viral disease that affects the liver. The disease ranges in severity from a mild illness lasting a few weeks to a serious, lifelong illness. HBV can be either “acute” or “chronic.” Acute HBV is a short illness (2-4 weeks) that occurs within the first 6 months after someone is exposed HBV. Acute infection may lead to chronic infection in a small percentage of cases. Chronic HBV infection is a long-term illness that occurs after acute infection if the virus continues to replicate (grow) in a person’s body.