2. SUBUNIT VACCINE
These are defined as those containing one
or more pure or semi pure antigens.
Usually it consist of specific, purified
macromolecules derived from pathogens.
e.g. HSV type 1 and 2, HIV-1, FMD,
Hepatitis-B vaccine
3. DISDVANTAGES
1) They generally requires strong adjuvants and
these adjuvants often induce tissue reaction.
2) Duration of immunity is generally shorter than the
live vaccines.
3) They often need to be linked to the carriers to
enhance immunogenicity
4) Several doses must be given for proper life-long
immunity.
4. PEPTIDE VACCINE
The vaccine in which peptide of the original pathogen is
used to immunize an organism.
The best known example is foot and mouth disease,
where protection was achieved by immunizing animals
with a linear sequence of 20 amino acids.
Synthetic peptide vaccines would have many
advantages. Their antigens are precisely defined and
free from unnecessary components which may be
associated with side effects.
They are stable and relatively cheap to manufacture.
Furthermore, less quality assurance is required.
Changes due to natural variation of the virus can be
readily accommodated, which would be a great
advantage for unstable viruses such as influenza.
5. CONT…….
Synthetic peptides do not readily stimulate T cells.
It was generally assumed that, because of their small size,
peptides would behave like haptens and would therefore
require coupling to a protein carrier which is recognized by T-
cells.
It is now known that synthetic peptides can be highly
immunogenic in their free form provided they contain, in
addition to the B cell epitope, T- cell epitopes recognized by T-
helper cells. Such T-cell epitopes can be provided by carrier
protein molecules, foreign antigens. or within the synthetic
peptide molecule itself.
Synthetic peptides are not applicable to all viruses. This
approach did not work in the case of polioviruses because the
important antigenic sites were made up of 2 or more different
viral capsid proteins so that it was in a concise 3-D
conformation.
6.
7. ADVANTAGE OF PEPTIDE VACCINE
Production and quality control simpler
No NA or other viral or external proteins, therefore
less toxic.
Safer in cases where viruses are oncogenic or
establish a persistent infection
Feasible even if virus cannot be cultivation
8. DISADVANTAGES
May be less immunogenic than conventional
inactivated whole-virus vaccines
Requires adjuvant
Requires primary course of injections followed by
boosters
Fails to elicit CMI.
