Investigation (in vivo and in vitro) of booster dose vaccine requirement for long-term protection against hepatitis B virus infection.

Materials and Methods: Seventeen individuals vaccinated previously were enrolled in the study. They had once developed a protective level of anti-HBs antibody after immunization and their anti-HBs titer had declined to an underprotective level. Twenty uninfected and unvaccinated healthy people were chosen as controls. Lymphoproliferative response to in-vitro stimulation with hepatitis B surface antigen (HBsAg) and anti-HBs response to vaccine were evaluated for immune response.