The number of injections of hepatitis B vaccine for adults is generally determined by the level of hepatitis B surface antibodies, and one injection of the vaccine is less immune stimulating than three injections of the vaccine, and the intensity of antibody production is lower. When the hepatitis B surface antibody is negative, it means that the body has no protection against hepatitis B. At this time, the risk of infection with the hepatitis B virus is higher, so three doses of hepatitis B vaccine should be given to stimulate the body to produce surface antibodies. When the hepatitis B surface antibody is weakly positive, the body has some immunity against hepatitis B, but the immunity is not too strong, so one dose of vaccine should be given intramuscularly to make the value of surface antibody higher. Therefore, the one-dose vaccine is suitable for people who have weak surface antibodies, while the three-dose vaccine is suitable for people who have no antibodies.