Hepatitis B is a virus which spreads through the blood and bodily fluids of an infected person. Hepatitis B is 100 times more infectious than HIV, with many people not even realising they have been infected with the virus. This is because symptoms may not develop immediately, or at all. The incubation period (time from coming into contact with the virus to developing the infection) is between one and six months. A blood test is carried out to detect the virus.

The virus is present in body fluids such as blood, saliva, semen and vaginal fluid. It can be passed from person to person, such as through unprotected sex (without using a condom) or by sharing needles to inject drugs. Infected mothers can also transmit the virus to their baby during childbirth (often without the woman being aware that she is infected).

The hepatitis B virus can go on to cause a chronic (long-term) illness, which follows an acute infection. This is very common in babies and young children, but it can also occur in adults. If you develop chronic hepatitis B, you may remain well, but you may pass on the virus because you are a carrier. Symptoms may come and go, or you may develop serious liver damage.

The occurrence of hepatitis B is highest in sub-Saharan Africa, south east Asia, and the Pacific Islands, such as the Hawaiian Islands, the Solomon Islands, and Fiji. The lowest incidence of hepatitis B is found in Australia, New Zealand, northern and western Europe, and North America. There are approximately 350 million carriers of the virus worldwide.

There is a vaccine available to protect against hepatitis B.