Subunit vaccine

A subunit vaccine is a vaccine that presents one or more antigens to the immune system without introducing pathogen particles, whole or otherwise. The antigens involved can be any molecule, and do not need to be a protein subunit; the word "subunit" simply means the antigen is a fragment of the pathogen. Just like inactivated vaccines, the vaccine is completely "dead", and is therefore less risky.[1]

Protein-based

One method of production involves isolation of a specific protein from a virus and administering this by itself. A weakness of this technique is that isolated proteins can be denatured. A second method of making a subunit vaccine involves putting an antigen's gene from the targeted virus or bacterium into another virus (virus vector), yeast (yeast vector), as in the case of the hepatitis B vaccine[2] or attenuated bacterium (bacterial vector) to make a recombinant virus or bacteria to serve as the important component of a recombinant vaccine (called a recombinant subunit vaccine). The recombinant vector that is genomically modified will express the antigen. The antigen (one or more subunits of protein) is extracted from the vector.[2] Just like the highly successful subunit vaccines, the recombinant-vector-produced antigen will be of little to no risk to the patient. This is the type of vaccine currently in use for hepatitis B,[2] and it is experimentally popular, being used to try to develop new vaccines for difficult-to-vaccinate-against viruses such as ebolavirus and HIV.[3]

Other subunits

Vi capsular polysaccharide vaccine (ViCPS) is another subunit vaccine, in this case, against typhoid caused by the Typhi serotype of Salmonella enterica.[4] Instead of being a protein, the Vi antigen is a bacterial capsule polysacchide, made up of a long sugar chain linked to a lipid.[5] Capsular vaccines like ViCPS tend to be weak at eliciting immune responses in children. Making a conjugate vaccine by linking the polysacchide with a toxoid increases the efficacy.[6]

Advantages and disadvantages

Advantages
  • Cannot revert back to virulence meaning they cannot cause the disease they aim to protect against[7][8]
  • Safe for immunocompromised patients[9]
  • Can withstand changes in conditions (e.g. temperature, light exposure, humidity)[7]

Disadvantages

References
  1. "MODULE 2 – Subunit vaccines". WHO Vaccine Safety Basics.
  2. "Recombivax". Retrieved May 5, 2013.
  3. Decker JM. "Vaccines". Immunology Course 419. Department of Veterinary Science & Microbiology at The University of Arizona. Archived from the original on 2003-06-10.
  4. Raffatellu M, Chessa D, Wilson RP, Dusold R, Rubino S, Bäumler AJ (June 2005). "The Vi capsular antigen of Salmonella enterica serotype Typhi reduces Toll-like receptor-dependent interleukin-8 expression in the intestinal mucosa". Infection and Immunity. 73 (6): 3367–74. doi:10.1128/IAI.73.6.3367-3374.2005. PMC 1111811. PMID 15908363.
  5. Hu X, Chen Z, Xiong K, Wang J, Rao X, Cong Y (August 2017). "Vi capsular polysaccharide: Synthesis, virulence, and application". Critical Reviews in Microbiology. 43 (4): 440–452. doi:10.1080/1040841X.2016.1249335. PMID 27869515.
  6. Lin FY, Ho VA, Khiem HB, Trach DD, Bay PV, Thanh TC, et al. (April 2001). "The efficacy of a Salmonella typhi Vi conjugate vaccine in two-to-five-year-old children". The New England Journal of Medicine. 344 (17): 1263–9. doi:10.1056/nejm200104263441701. PMID 11320385.
  7. Baxter D (December 2007). "Active and passive immunity, vaccine types, excipients and licensing". Occupational Medicine. 57 (8): 552–6. doi:10.1093/occmed/kqm110. PMID 18045976.
  8. Moyle PM, Toth I (March 2013). "Modern subunit vaccines: development, components, and research opportunities". ChemMedChem. 8 (3): 360–76. doi:10.1002/cmdc.201200487. PMID 23316023.
  9. Vartak A, Sucheck SJ (April 2016). "Recent Advances in Subunit Vaccine Carriers". Vaccines. 4 (2): 12. doi:10.3390/vaccines4020012. PMC 4931629. PMID 27104575.


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