Despite the availability of
hepatitis A vaccines that might provide protection for decades,
hepatitis B vaccines that provides protection for at least 15 years and the recent introduction of a combined
hepatitis A and B
vaccine, these
infections continue to spread in both the developed and developing world.
Hepatitis A vaccine coverage has been limited to high-risk groups: such a selective immunisation policy is unlikely to have a major impact. If adequate immunogenicity in infants is confirmed, dosing schedules can be improved and the costs of vaccination reduced, universal paediatric immunisation with combined
hepatitis A and B products is likely to result in the eventual eradication of these
infections. In the interim, novel
hepatitis A vaccines are being investigated and additional studies on
hepatitis A vaccine immunogenicity in infants are in progress. Worldwide use of
hepatitis B vaccines for the newborn, young children and high-risk groups should control this
infection and obviate the need for a
vaccine against
hepatitis D. Newer
hepatitis B vaccines that may reduce the likelihood of non-responsiveness and have immunotherapeutic value are under study. A recombinant
hepatitis E vaccine for use in endemic regions is currently in clinical trials. The development of an effective
hepatitis C vaccine has been agonisingly slow and many impediments have been recognised. These include the lack of a susceptible small animal, a high degree of hepatitis C virus (HCV) genomic diversity and failure to produce high quantities of HCV in tissue culture. The development of a novel HCV replicon system may be a major breakthrough. Nonetheless, it may still be exceedingly difficult to produce a
vaccine that uniformly provides sterilising immunity; the possibility of developing a
hepatitis C vaccine that can prevent
chronic infection is an exciting concept that requires further investigation. Advances in recombinant technology, the use of novel genetic (
DNA-based)
vaccines, expression of
hepatitis antigens in plants and improved adjuvants also hold considerable promise.