New approaches to hepatitis A and B vaccines.

Plasma-derived vaccines and yeast-derived recombinant vaccines against hepatitis B virus (HBV) infection have gained an acceptable record of efficacy. However, non- or hyporesponsiveness to immunization does not only occur in cases of obesity, renal failure or immune suppression, but also in healthy individuals. There is therefore a rationale for developing more immunogenic vaccines against HBV, especially for those populations who are potential non- or hyporesponders. Currently used recombinant hepatitis B vaccines consist of antigen particles assembled with the product of 226 amino acids encoded in the S gene. Since proteins encoded in the pre-S gene are also incorporated in the HBV envelope, pre-S gene products should, at least in theory, be useful in improving protection with hepatitis B vaccines. Inactivated hepatitis A vaccines are more potent than currently used hepatitis B vaccines. Two injections of a standard dose of HAVRIX (SB) by the intramuscular route, or even a single injection using a higher dose (HAVRIX 1440), will achieve protective levels of antibodies. Therefore, increased potency is not essential with inactivated hepatitis A vaccines. New hepatitis A vaccines are likely to be recombinant or attenuated live types. Another aspect of the improvement of existing hepatitis A and B vaccines is unification into a combined form.