Hepatitis B is a liver infection caused by the hepatitis B virus (HBV). While it is found worldwide, it is most prevalent in East Asia and Sub-Saharan Africa. The virus spreads through direct contact with the blood or bodily fluids of an infected person, with higher rates of infection in regions such as East Asia, Sub-Saharan Africa, the Amazon, southern, eastern, and central Europe, the Middle East, and the Indian subcontinent.

In some cases, acute hepatitis B can lead to severe liver damage, including fulminant hepatic necrosis, which can be fatal.

The virus is transmitted through infected body fluids, such as during vaginal or anal intercourse, needle sharing, or from mother to child during childbirth.