VMC 221: Veterinary Immunology and Serology (1+1)

SUBUNIT VACCINES/CONJUGATE VACCINES

• It is possible to identify the peptide sites encompassing the major antigenic sites of viral antigens, from which highly purified subunit vaccines can be produced. But increasing purification may lead to loss of immunogenicity, and this may necessitate coupling to an immunogenic carrier protein or adjuvant.
• Example of a purified subunit vaccine is HA vaccines for influenza A and B. Bacterial capsular polysaccharides are immunogenic but incapable of evoking T cell responses.
• Vaccines efficacy can be greatly increased by conjugating the capsular polysaccharide to a protein carrier capable of supply of T cell epitopes called a conjugate vaccine.
• Advantages
  • Avoids use of whole organism
  • Side effects due to undesired part of the organism is reduced
  • Supplies multiple epitopes.
• Disadvantages
  • Possible alteration of pathogen protein conformation during purification may decreases immunogenicity
  • Can be laboured intensive and costly to purify immunogens
  • May require cold chain
  • Sometimes too large to fit into the vaccine delivery systems.