According to the World Health Organization, hepatitis B virus (HBV) is an important risk factor for liver cancer and cirrhosis. Currently, two billion people are infected with HBV, and 350 million people have long-term effects resulting from the virus. For example, approximately one quarter of adults that were infected with HBV as children ultimately die from liver cancer and cirrhosis. An effective method to prevent HBV infection and its subsequent long-term health effects is through immunization with the hepatitis B vaccine.
In 2004, an estimated 350 million individuals were infected worldwide. National and regional prevalence ranges from over 10% in Asia to under 0.5% in the United States and northern Europe. Routes of infection include vertical transmission (such as through childbirth), early life horizontal transmission (bites, lesions, and sanitary habits), and adult horizontal transmission (sexual contact, intravenous drug use). The primary method of transmission reflects the prevalence of chronic HBV infection in a given area. In low prevalence areas such as the continental United States and Western Europe, injection drug abuse and unprotected sex are the primary methods, although other factors may also be important. In moderate prevalence areas, which include Eastern Europe, Russia, and Japan, where 2–7% of the population is chronically infected, the disease is predominantly spread among children. In high prevalence areas such as China and South East Asia, transmission during childbirth is most common, although in other areas of high endemicity such as Africa, transmission during childhood is a significant factor. The prevalence of chronic HBV infection in areas of high endemicity is at least 8%. As of 2010, China has 120 million infected people, followed by India and Indonesia with 40 million and 12 million respectively. According to WHO, an estimated 600,000 people die every year related to the infection.