Hepatitis B vaccine has poor immunity against mutated hepatitis B. Hepatitis B virus belongs to DNA virus and may mutate in the process of continuous replication. Ordinary hepatitis B vaccine may have certain immunity against mutated hepatitis B virus, but the immunity is relatively poor, and people who have received hepatitis B vaccine may still be infected when they come into contact with mutated hepatitis B virus. However, since there are relatively few mutated hepatitis B viruses, the probability of infection is relatively low. In addition, hepatitis B surface antibody belongs to protective antibody, with the prolongation of time, the antibody titer will gradually decrease, or even disappear, and can not play a protective role, so it is recommended to recheck hepatitis B 5 every year, and if the antibody titer decreases, inject hepatitis B vaccine booster injection under the guidance of the doctor if necessary.