5 Jun

Vaccines for several other viral diseases are  currently in the early stages of development. At  least four  different types of hepatitis C vaccines are  in preclinical development. However, research for these candidate vaccines is hampered by the  lack of reproducible tissue culture or  a  convenient small animal model  for  testing (212).  Early studies in  chimpanzees with several hepatitis C vaccines are  currently underway.

Three different Epstein-Barr  virus vaccine types are reported to be in phase I studies, including a glycoprotein sub- unit (gp350)  vaccine, a vaccinia recombinant vaccine express- ing gp350, and  peptide induction of cutaneous T lymphocytes (212). It is yet unknown if the  specific  antigenic components of these vaccines are  sufficient to prevent infection.

At least 14 different vaccines are  under development for dengue virus. While  most  are  in preclinical stages, a combined quadrivalent vaccine is in phase I trials. The  live-attenuated vaccines have shown encouraging promise in the prevention of infection (212).

Viral  vaccine development continues to move  away from classical live-attenuated  vaccines towards whole  inactivated virus vaccines, peptide-based vaccines, DNA-based vaccines, use  of viral vectors to insert recombinant information in vac- cines,  human immune globulins, monoclonal antibodies, and recombinant humanized vaccines, such  as product production standardization, sustained immunological response, technical feasibility, less  reactogenic, and  nontransmissable or  non- pathogenic to humans. However, there are  challenges to the use  of these new  technologies, such  as  reliable efficacy  and potency, need  for  an  adjuvant or  delivery system, or  estab- lishement of proof of principal.

Perhaps the  greatest challenge is the  expectation that a vaccine will be 100% effective and  safe for every  vaccinee. One death among 1 million vaccinees is considered excessive. How- ever, without the  vaccine, many more  may  die  from  the  dis- ease. Such  is  the  case  with the  withdrawn approval of the rotavirus vaccine, when up to 600,000 children from developing countries die each  year from dehydration and  diarrhea. Adju- vants enhance the  effect of the  vaccine and  may  permit lower dosage levels  and  lower  number of dosages. They  may  provide better mucosal immunity, more  protection for  the  immuno- compromised, and  better antibody response (326).

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