The Hepatitis B virus (HBV) is a small (3200 base pair) DNA virus with a viral envelope. HBV replicates in the liver cells of humans and other higher primates, and produces an excess of the viral envelope protein (Hepatitis B surface antigen, HBsAg) that circulates in the blood. HBV is transmitted by percutaneous and permucosal exposure to infected blood or other body fluids, including semen and vaginal fluids. In highly endemic areas, HBV is most commonly spread from mother to child at birth, or from person to person in early childhood. It has a worldwide distribution and currently more than 2 billion persons have been infected, with approximately 360 million chronically infected. The outcomes of HBV infection are age-dependent and persons with chronic HBV infection have a 15-25% risk of dying prematurely from HBV-related causes include hepatitis, liver cirrhosis, and hepatocellular cancer.
Hepatitis B Vaccines
The first hepatitis B vaccine to become available commercially in 1982 consisted of HBsAg purified from the plasma of persons with chronic HBV infection. Following stringent inactivation procedures the purified HBsAg was formulated with an adjuvant and for multi-dose vials, thiomersal was added as a preservative. This vaccine has now been replaced by recombinant vaccines that are free of any concerns associated with human blood products. The HBsAg gene has been inserted into yeast and mammalian cells by means of appropriate expression vectors. Antigen expressed in several species of yeast, namely Saccharomyces cerevisiae, Pichia pastoris and Hansenula polymorpha, and Chinese hamster ovary (CHO) cells has been used to produce hepatitis B vaccines for over 20 years.
The recombinant HBsAg particle differs from the native particle only in the glycosylation of the protein, which can vary according to the production cell. Purified antigen has been shown to induce antibodies in mice and guinea-pigs and to protect chimpanzees from infection with hepatitis B virus. Following purification from host-cells components, the HBsAg is adsorbed to alum (aluminium hydroxide or aluminium phosphate) and depending on the vaccine formulation an additional adjuvant and preservatives may be added. The protective efficacy of Hepatitis B vaccination is related to the induction of antibodies directed against HBsAg. An antibody titer of ≥10 mIU per ml measured 1-3 months after the administration of the last dose of the primary vaccination series is considered a reliable marker of protection against infection. Hepatitis B vaccine in combination with DTP are increasingly being used in national immunization campaigns.
Hepatitis B Vaccine Standardization
The WHO requirements for the first plasma-derived Hepatitis B vaccine were first formulated in 1980 and revised in 1987. These requirements will continue to be in force until plasma derived vaccine is no longer manufactured.
Requirements for Heptatitis B Vaccine prepared from Plasma, Annex 8, Technical Report Series No. 771, 1988
The WHO requirements for Hepatitis B vaccines made by recombinant DNA techniques were adopted in 1988 and amended in 1997 to allow the replacement of the animal potency test with an in vitro test. They were revised in 2010 to update the manufacturing and quality control information; and to include new sections addressing nonclinical and clinical evaluation of recombinant hepatitis B vaccines.
Recommendations to Assure the Quality, Safety and Efficacy of Recombinant Hepatitis B Vaccines. Replacement of Annex 2, TRS 786 and Annex 4, TRS 889. Technical Report Series 978, Annex 4
Because of diversity in the reactivity of vaccines containing HBsAg produced by different manufacturing processes and to which adjuvants have been added by different methods, a single reference material is not suitable for the standardization of hepatitis B vaccines in in vivo or in vitro assays. Manufacturers therefore are required to establish a product specific reference preparation which is traceable to a lot of vaccine shown to be efficacious in clinical trials.
Prequalified Hepatitis B vaccines
Recombinant hepatitis B vaccines, both monovalent and in combination with DTwP and DTwP Hib are prequalified for procurement by UN organizations: