The synthetic peptide approach to vaccine development arose in response to rapid DNA cloning and sequencing technology. This made it possible to quickly obtain primary sequences and construct various peptides.
Major efforts were put into the development of a synthetic vaccine (a linear sequence of 20 amino acids) for foot-and-mouth disease virus (FMDV) for which even today no alternative exists besides the classical vaccine based on inactivated virus.
Since synthetic peptide antigens are precisely defined and free from unnecessary components which may be associated with side effects, vaccines made with synthetic peptides have many advantages. 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.
It is generally assumed that, “synthetic peptides do not readily stimulate T cells because of their small size. It is now known that synthetic peptides can be highly immunogenic in their free form provided they contain T- cell epitopes, in addition to the B cell epitopes, to get recognized by T-helper cells.
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 polio viruses because; the important antigenic sites were made up of 2 or more different viral capsid proteins so that it is in a concise 3-D conformation.