The hepatitis B virus (HBV for short) is the virus that causes the illness hepatitis B. Transmission of the hepatitis B virus occurs when blood, semen, or other body fluid from an infected person enters the body of a person who is not infected, such as through having sex with an infected person or sharing needles or drugs with people who are infected. Some people who are exposed to the hepatitis B virus are unable to get rid of it. These people develop a long-term liver infection known as chronic hepatitis B, which can eventually lead to liver cancer, liver failure, and even loss of life. An estimated 70,000 Americans become infected with chronic hepatitis B in a typical year. About 5,000 of these people will die of the complications caused by the disease.