Hepatitis B virus (HBV) is a highly contagious viral infection that can cause liver damage. The virus is easily spread via hep B–positive blood, semen or other body fluid. Pregnant women who have hepatitis B can also transmit the virus to their babies, usually during birth. People who have not been infected with HBV can be vaccinated against the virus to prevent infection.

There are two phases of hepatitis B infection: acute and chronic. Acute refers to a new infection that is less than six months old; an HBV infection that lasts more than six months is chronic. Acute hepatitis B will resolve on its own without serious complications in the majority of newly infected teens and adults. When this occurs, people are no longer contagious and are immune to further HBV infections. However, in people whose infection does not resolve, HBV may be transmitted to others. Chronic hep B can cause fibrosis (mild to moderate liver scarring), cirrhosis (serious liver scarring), liver cancer, liver failure and death.

The risk that a hepatitis B infection will become chronic varies according to the age at the time of infection. In the United States, approximately 90 percent of infants and 25 to 50 percent of children under the age of 5 years will remain chronically infected with HBV. In adults, roughly 95 percent recover completely.

Because of routine HBV vaccination, the number of new hepatitis B infections in the United States has declined from about 260,000 a year in the 1980s to nearly 20,000 in 2013, with the greatest decline occurring in children and adolescents.

Worldwide, more than 2 billion people have been infected with hepatitis B at some point, resulting in 350 million people with chronic infections. Nearly 786,000 people die from HBV-related liver disease each year. According to the Centers for Disease Control and Prevention (CDC), an estimated 700,000 to 1.4 million people in the United States have chronic HBV infection, with nearly 1,900 hepatitis B–related deaths in 2013.

Last Revised: July 15, 2010