The factors influencing the immune response to hepatitis B vaccine and persistence of the protection.

 Hepatitis B virus (HBV) infection and its sequelae which include cirrhosis and hepatocellular carcinoma is a major public health problem throught the world.The WHO strategy for effective control of HBV infection is vaccination with the surface antigen of virus(HBsAg).The results obtained from a large number of studies demonstrated that the vaccine induces a protective antibody resonse (anti-HBs > 10 IU/L) in the majority of vaccinees,but 1-10% of subjecte fail to repond.This unresponsiveness to HBsAg    has been attributed to a variety of mechanisms including expression of certain HLA antigens and haplotypes, defect in HBsAg-specific T-cell and B-cell repertoire , defect in antigen presenting cell function, immunological tolerance and imbalance in T helper cell function. Furthermore immunization factors that influence immunogenicity include    type of vaccine dosage ,number and timing of injections, site and route of injections.Host factors such as sex, age weight ,genetics,immunological competency of the host and smoking also may influence the immune response to HB vaccine.The level of anti-HBs dose wane after vaccination.This phenomenon has fuctional significance for booster vaccination.In this review article the factor that affect the immunogenicity of HB vaccine,immunological basis of unresponsiveness to vaccine and persistence of protection were evaluated.    Key words. Hepatitis B vaccine, Immunogenicity, Unresponsiveness, Anti-HBs antibody