Hepatitis B is an infectious disease caused by the Hepatitis B virus (HBV) that affects the liver; it is a type of viral hepatitis. It can cause both acute and chronic infection.Many people have no symptoms during an initial infection. For others, symptoms may appear 30 to 180 days after becoming infected and can include a rapid onset of sickness with nausea, vomiting, yellowish skin, fatigue, dark urine, and abdominal pain. Symptoms during acute infection typically last for a few weeks, though some people may feel sick for up to six months. Deaths resulting from acute stage HBV infections are rare. An HBV infection lasting longer than six months is usually considered chronic. The likelihood of developing chronic hepatitis B is higher for those who are infected with HBV at a younger age. About 90% of those infected during or shortly after birth develop chronic hepatitis B, while less than 10% of those infected after the age of five develop chronic cases. Most of those with chronic disease have no symptoms; however, cirrhosis and liver cancer eventually develop in about 25% of those with chronic HBV.The virus is transmitted by exposure to infectious blood or body fluids. In areas where the disease is common, infection around the time of birth or from contact with other people's blood during childhood are the most frequent methods by which hepatitis B is acquired. In areas where the disease is rare, intravenous drug use and sexual intercourse are the most frequent routes of infection. Other risk factors include working in healthcare, blood transfusions, dialysis, living with an infected person, travel in countries with high infection rates, and living in an institution. Tattooing and acupuncture led to a significant number of cases in the 1980s; however, this has become less common with improved sterilization. The hepatitis B viruses cannot be spread by holding hands, sharing eating utensils, kissing, hugging, coughing, sneezing, or breastfeeding. The infection can be diagnosed 30 to 60 days after exposure. The diagnosis is usually confirmed by testing the blood for parts of the virus and for antibodies against the virus. It is one of five main hepatitis viruses: A, B, C, D, and E. During an initial infection, care is based on a person's symptoms. In those who develop chronic disease, antiviral medication such as tenofovir or interferon may be useful; however, these drugs are expensive. Liver transplantation is sometimes recommended for cases of cirrhosis or hepatocellular carcinoma.Hepatitis B infection has been preventable by vaccination since 1982. As of 2022, the hepatitis B vaccine is between 98% and 100% effective in preventing infection. The vaccine is administered in several doses; after an initial dose, two or three more vaccine doses are required at a later time for full effect. The World Health Organization (WHO) recommends infants receive the vaccine within 24 hours after birth when possible. National programs have made the hepatitis B vaccine available for infants in 190 countries as of the end of 2021. To further prevent infection, the WHO recommends testing all donated blood for hepatitis B before using it for transfusion. Using antiviral prophylaxis to prevent mother-to-child transmission is also recommended, as is following safe sex practices, including the use of condoms In 2016, the WHO set a goal of eliminating viral hepatitis as a threat to global public health by 2030. Achieving this goal would require the development of therapeutic treatments to cure chronic hepatitis B, as well as preventing its transmission and using vaccines to prevent new infections.An estimated 296 million people, or 3.8% of the global population, had chronic hepatitis B infections as of 2019. Another 1.5 million developed acute infections that year, and 820,000 deaths occurred as a result of HBV. Cirrhosis and liver cancer are responsible for most HBV-related deaths. The disease is most prevalent in Africa (affecting 7.5% of the continent's population) and in the Western Pacific region (5.9%). Infection rates are 1.5% in Europe and 0.5% in the Americas. According to some estimates, about a third of the world's population has been infected with hepatitis B at one point in their lives. Hepatitis B was originally known as "serum hepatitis".