Vaccination Against Hepatitis B Virus: Past and Future Problems

Abstract

The possibility of immunization against hepatitis B virus (HBV) originated with B.S. Blumberg [1] who, in 1967, established the existence of a relationship between infection by HBV and the presence in the blood of an antigen of lipoprotein nature. This circulating antigen was eventually identified as the major constituent, or a major constituent, of the viral envelope, and was found to be discharged in great quantities into the blood. There is still no clear understanding of this mechanism. A considerable quantity of viral material, labelled HBs antigen (HBsAg) and occurring in the viral envelope, is secreted as if, in the hepatocyte where the virus replicates itself, it did not encounter the internal viral structures or the elements permitting assembly of the complete virus. In this respect, infection by HBV is unique. Other antigens may be liberated into the blood in viral infections, but their levels remain very low and the duration of their presence is limited. On the other hand, infection with HBV may lead to discharge into the blood of amounts of HBsAg 100 to 1000 times greater, levels possibly reaching 200–300 μg/ml. Moreover, infection with this virus has the special property that some individuals become chronic carriers of virus with or without pathological manifestations and therefore harbour more or less significant amounts of HBsAg in their serum. This condition is particularly common in immunodepressed patients, notably those on haemodialysis.