Soon after HBV enters the body, it infects cells in the liver called hepatocytes. In response to this infection, the immune system targets the virus and the hepatocytes already infected with the virus. This causes inflammation of the liver (hepatitis).
HBV can cause acute hepatitis, meaning short-term inflammation of the liver, until the immune system is able to clear the virus from the body, usually within six months of becoming infected with the virus. However, HBV can become a chronic infection.
This means that the immune system is not able to get rid of the virus within six months after infection. In other words, the virus continues to reproduce in the person’s liver for several months or years after infection. This can increase the risk of liver damage and liver cancer. What’s more, someone with chronic HBV infection can transmit the virus to others.
The risk of chronic infection depends highly on whether a person is infected as an infant, child or adult. About 90 percent of infants infected with HBV go on to experience chronic hepatitis B. Between 25 to 50 percent of children ages 1 to 5 who are infected with HBV will remain chronically infected with the virus. By contrast, nearly 95 percent of adults recover completely from HBV infection and do not become chronically infected.
Some adults infected with HBV are more likely to clear the virus during the acute phase of the infection than others. For example, patients who have impaired immune responses, who are recovering from organ transplants, who are undergoing chemotherapy or dialysis for kidney problems, who are receiving steroid therapy to suppress the immune system, or who are HIV positive are more likely to develop chronic HBV infection than patients with normal immune responses.