Hepatitis B vaccine. Kids get 3 shots before age 1. Immunity is known by taking antibody titer. If you are a dentist or medical personnel you can get the adult hepatitis b given 3x again.
Failure? There are some individuals who apparently do not have the capacity to produce antibodies to hepatitis b surface antigen. These are the people who develop chronic hepatitis following acute infection. If you are in this category you may be at risk. On the other hand, if you have received the vaccine and not turned hep b antibody positive you might want to try once more.
Herd Immunity. This is why universal immunization is a good idea: your chances of catching hepatitis are much lower because most people are immune, and cannot get you sick.