Hepatitis B is a viral infection of the liver. Along with other hepatitis types (such as hepatitis C and hepatitis E), hepatitis B is caused by transmission (spread) of the virus through blood and body fluids. Some persons infected with hepatitis B develop a chronic infection, become carriers, and are then able to pass on the infection to others. All individuals with hepatitis B are at higher risk of developing liver cancer and cirrhosis of the liver. Hepatitis A is a less serious type of viral liver infection that is transmitted by the fecal-oral route (by contaminated water, food, surfaces, and hands). Hepatitis B affects more than 300 million individuals worldwide and is a serious health problem in many industrialized nations and developing countries. Most people who have chronic hepatitis B were infected at birth or in early childhood. The April 13, 2011, issue of JAMA includes an article about hepatitis B vaccine.