Food and Drug Administration: Who's at risk; Why we vaccinate infants and children
“Hepatitis B is a viral disease transmitted through blood and body fluids. In its acute phase it can cause liver failure and death. It can also become chronic, causing liver damage, including cancer, over a number of years.
Except for infants born to mothers with this infection, children are not at great risk of developing hepatitis B, but health-care workers, homosexuals, and intravenous drug users are. Attempts to vaccinate adults have been largely unsuccessful, however.
It's easier to reach children because school enrollment requires immunization. Therefore, for lifelong protection, CDC has recommended that all infants be vaccinated before 15 months of age in three doses. There are no serious reactions to the vaccine."