The hepatitis B vaccine used in China is an inactivated blood-derived vaccine, and just one injection does not produce sufficient immune protection. Studies have shown that three doses, as prescribed, can produce immunity in more than 95% of adolescents and adults. The first and second doses of the vaccine are known as sensitization vaccinations, which produce antibodies, and the third dose is known as booster immunizations, which produce antibodies of higher potency and have a more lasting preventive effect. After three doses of hepatitis B vaccine, the immunity (protection) can generally be maintained for about five years, and the hepatitis B half test should be repeated in about 4-5 years, so that if the antibody titer of hepatitis B virus is still strong, another booster vaccination can be given. If the antibody titer of hepatitis B virus is weak or completely disappeared, three doses of hepatitis B vaccine should be re-administered to make the body produce hepatitis B virus antibody again.