Indian Pediatrics 2001; 38: 797  

Antigens in Hepatitis B Vaccines

The new generation plasma derived Hepatitis B vaccine is said to have both Pre S1 and Pre S2 protein along with S antigen (all major molecular species in Pre S1 Pre S2 and S Ag), whereas other plasma derived and genetically engineered vaccines contain only S antigen protein (S Ag). Is the claim that this new generation vaccine enhances immuno-genecity valid?

Global experience on hepatitis B immunization has been spread over nearly 2 decades and millions of persons vaccinated. Success in protection and the immunogenicity and safety records have been excellent. The original, past and current vaccines are all based on the outer layer protein component of the virus. This components is essentially the surface antigen (HBsAg), derived from human plasma or produced in vector cells such as E. coli, different yeast species or certain mammalian cell cultures. The surface antigen and its encoded genomic region is flanked by pre-s peptides or their genome sequences. The presence or absence of the pre-s peptides, either pre-s 1 or pre-s 2 or both, has not made any important impact on the success of vaccination.

All plasma-derived HBsAg contains the pre-s components, but they are usually lost or drastically reduced during processing, puri-fication, or inactivation of residual virus, if any, in the production of the vaccine. Some processing techniques may preserve the pre-s components. One such example has been quoted in the question itself.

The genetically engineered vaccines may also contain the pre-s 1 or pre-s 2 peptides, provided the genomic sequence introduced into the vector contained the necessary gene-tic segments. There is some evidence that the presence of pre-s components may increase the immunogenic property of a vaccine. Such increase may result in higher antibody levels, or reduced incidence of vaccine unres-ponsiveness. Since neither issue is very relevant in pediatric immunization, the debate on the merits of such vaccines is not critical. Moreover, data are insufficient as of now to show clearly that every vaccine with pre-s is more immunogenic than the currently available, highly immunogenic vaccines, containing no pre-s.

I do realize that I have not given a clear answer. In pediatric practice, reliable pro-ducts, supply under cold chain, past informa-tion on immunogenicity, lower cost and ready availability are more important than whether a particular product contains pre-s 1 or pre-s 2 or no pre-s component at all. Will any one take up the challenge to evaluate the compara-tive immunogenicities of different vaccines in children and in adults?

T. Jacob John
Emeritus Medical Scientist (ICMR), 439,
Civil Supplies Godown Lane, Kamalakshipuram, Vellore TN 632 002,
India. E-mail: [email protected]