One shot of Hepatitis B vaccine has antibodies, but the antibody titer is low and normally does not normally work as a preventive measure. Hepatitis B vaccine is a vaccine to prevent hepatitis B virus infection, and under normal circumstances, three injections are required. After the first injection, the body enters the induction phase, and the first vaccine only enters the body as a small dose of specific antigen, stimulating the body to produce immune response cells. At this time, the body usually only produces a very small portion of antibodies, the antibody titer is relatively low, and the maintenance time in the body is also very short, usually does not play a preventive role. Usually it is necessary to receive the second injection after 1 month, after the second injection will enter the body cellular immunity enhancement phase, at this time the body will produce a large number of antibodies, which has a certain preventive effect. After the completion of the second injection, a third injection is needed to enter the strengthening stage, so that the antibody potency will be increased and the maintenance effect will be more lasting. To summarize, one shot of hepatitis B vaccine will produce a small amount of antibody, but the antibody maintenance time is short and the preventive effect is not big. It is recommended that patients should strictly receive three injections according to the regulations in order to achieve better preventive effect.