Hepatitis B is a vaccine-preventable liver infection caused by the hepatitis B virus (HBV).

Hepatitis B is spread when blood, semen, or other body fluid infected with the hepatitis B virus enters the body of someone who is not infected. It is not spread through food or water, sharing eating utensils, breastfeeding, hugging, kissing, hand holding, coughing or sneezing.

Hepatitis B manifests in two ways: acute (short-term) infections that come from exposure to the HBV virus, and chronic (long-term) infections which occur when the body is not able to clear the HBV. Acute HBV infections occur within the first six months after exposure and the virus is cleared from the body after an illness of short duration. Chronic HBV occurs when the body fails to clear the virus. This happens more often in younger people. About nine in ten infants who become infected go on to develop life-long, chronic infections. The risk goes down as the child gets older. About one in three children who get infected before age 6 will develop chronic hepatitis B. By contrast almost all older children and adults infected with the virus recover completely.