The recent developments in modern vaccinology are mainly based on: (i)
cloning of microbial genes into recombinant vectors containing genetic
information for expression of desired neutralizing immunogens; (ii)
alternatives of attenuated vectors with deleted genes permitting the
insertion of several foreign genes expressing antigens exposed to the
host immune system during the abortive replication of such vectors;
(iii) combined vaccines with the aim to protect against many diseases
with a limited number of administrations; (iv) evidence demonstrating
the ability of animals to respond serologically to DNA injections
considered as a potential method of vaccination; (v) the possibility to
manipulate the immune system with new and improved immunomodulators
enhancing the immune response; and (vi) new microcarrier systems for
particular immunogens or immunomodulators delivery, either in a single
dose or sustained release, and presentation to the immune system for a
relevant response. New vaccines being developed are mainly based on
viral, bacterial or other vectors modified with genetic engineering
technology, to possess and express desired antigens for vaccination
against single or multiple infections. Existing combined vaccines like
diphtheria, tetanus, pertussis (DTP) are also experimented with new
additional components like recombinant hepatitis B virus surface
antigen, inactivated poliovirus, and Haemophilus inJluenzae type b
immunogens, in order to produce multivalent vaccines. Such types of
vaccines permitting the reduction of multiple medical visits is of
particular interest to pediatric immuni- zation programs, and would
benefit especially the developing countries assuring better vaccine
compliance with immunization schedules.
