Worldwide, most hepatitis B infections are found in children. Young children are the ones most likely to develop a lifelong, or chronic, infection. The risk of such an infection is small for children older than four years.
About ninety percent of babies infected with hepatitis B during the first year develop chronic infections. Such persons are at high risk of death from liver disease or liver cancer. The hepatitis B vaccine is considered to be the first medicine that can protect people against liver cancer.