The hepatitis B surface antibody is low for the following reasons: 1, close contact with hepatitis B carriers in daily life, precisely because of constant contact with the hepatitis B virus, the body will be able to neutralize the hepatitis B virus through hepatitis B antibodies, it will be able to consume the antibodies in the body, so there will be a decline in antibody values. 2, the cellular immune function is not sound enough, especially seen in children and adolescents, the immune function is still in the process of development, unlike The hepatitis B vaccine can only produce relatively small titers of antibodies after it has been administered. 3. The body is in a period of low cellular immunity, such as recently having tuberculosis, or having used immunosuppressive drugs such as hormones, azathioprine, cyclophosphamide, etc., when the hepatitis B vaccine cannot stimulate the body to produce high enough hepatitis B antibodies. 4. There may be quality problems with the hepatitis B vaccine itself. The hepatitis B vaccine needs to be transported in the cold chain, and as long as there is a link in the transportation process where the temperature control is not in place, it will lead to partial inactivation of the hepatitis B vaccine, so the human body will not be able to produce high-valent hepatitis B antibodies after using it.