If the antibody is still positive after 20 years of hepatitis B vaccination, such antibody is the protective antibody produced by the body, but if the antibody is weak, it is necessary to receive hepatitis B vaccine in time. After receiving hepatitis B vaccine, the body will produce protective antibodies, thus achieving the purpose of preventing hepatitis B virus infection. However, with the passage of time, the number of protective antibodies produced by the body will gradually decrease. If the antibody is still positive after 20 years of hepatitis B vaccination, the protective effect of the antibody and the titer of the antibody may be very low, and the effect of preventing hepatitis B cannot even be achieved. Different people have different physical conditions, and the maintenance time of antibody produced after vaccination is also different. To know the antibody titer in the body, you can check it regularly, and when the antibody titer is too low, you can take hepatitis B vaccine again. If you feel unwell after hepatitis B vaccination and don’t feel relieved, you should consult a doctor in time and find out the cause under the doctor’s guidance and then treat it actively to avoid delaying the condition.