How long vaccine antibodies last depends on the type of vaccine, the immunization period of the vaccine, and the immunity of the body. Vaccines can be broadly divided into inactivated vaccines, attenuated vaccines, recombinant vaccines, etc. The duration of immunity varies from one vaccine to another, as do the types of diseases to which they are immunized. For example, the immunization period of hepatitis B vaccine can reach 12 years, the immunization period of influenza vaccine is only 6-10 months, and the immunization period of MMR vaccine is about 8-9 years. In some vaccines, the titer of antibodies decreases or even disappears after the immunization period and requires revaccination. The level of antibodies produced by the vaccine depends on the immunity of the body. If the immunity of the body is weak, the titer of antibodies will be lower and the duration of maintenance will be shorter. In the case of people with low immunity, such as AIDS patients, patients with malignant tumors or patients with long-term hormone application, the level of antibody production is especially low, even if it does not produce effective protection. Therefore, for some vaccinations, the first dose should be doubled for immunocompromised people, for example, the first dose of rabies vaccination should be doubled.