A subunit vaccine is a vaccine that contains purified parts of the pathogen that are antigenic, or necessary to elicit a protective immune response. A "subunit" vaccine doesn't contain the whole pathogen, unlike live attenuated or inactivated vaccine, but contains only the antigenic parts such as proteins, polysaccharides or peptides. Because the vaccine doesn't contain "live" components of the pathogen, there is no risk of introducing the disease, and is safer and more stable than vaccine containing whole pathogens. Other advantages include being well-established technology and being suitable for immunocompromised individuals. Disadvantages include being relatively complex to manufacture compared to some vaccines (such as RNA vaccine), possibly requiring adjuvants and booster shots, and requiring time to examine which antigenic combinations may work best.
Subunit vaccines contain fragments of the pathogen, such as protein or polysaccharide, whose combinations are carefully selected to induce a strong and effective immune response. Because the immune system interacts with the pathogen in a limited way, the risk of side effects is minimal. An effective vaccine would elicit the immune response to the antigens and form memory that allows quick recognition of the pathogens and quick response to future infections.
A drawback is that the specific antigens used in a subunit vaccine may lack pathogen-associated molecular patterns which are common to a class of pathogen. These molecular structures may be used by immune cells for danger recognition, so without them, the immune response maybe weaker. Another drawback is that the antigens do not infect cells, so the immune response to the subnit vaccines may only be antibody-mediated, not cell-mediated, and as a result, is weaker than those ellicited by other types of vaccines. To increase immune response, adjuvants may be used with the subunit vaccines, or booster doses may be required.
|Protein subunit||contains isolated proteins from pathogens (virus or bateria)||hepatitis B, acellular pertussis vaccines|
|Polysaccharide||contains chains of polysaccharides (sugar molecules) found in the pathogen's capsule such as cell walls of some bacteria||pneumococcal polysaccharide vaccine, meningococcal vaccine preventing diseases from Neisseria meningitidis group A, C, W-135, and Y|
|Conjugate||contains polysaccharide chains bound to carrier proteins, such as diphtheria and tetanus toxoid, to boost the immune response||pneumococcal conjugate vaccine, haemophilus influenzae type b conjugate vaccine, meningococcal conjugate vaccine|
This section may be confusing or unclear to readers. In particular, the term 'vector' in this section may be used with different meanings. For example, virus vector means using another virus as a vector to carry gene into cell, whereas yeast vector means using another vector to carry gene into the yeast. The primary reference used in this section is 'Recombivax' page which doesn't used the term 'vector' at all. (August 2021)
This section needs additional citations for verification. (August 2021)
One method of production of protein-based subunits 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 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. 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, and it is experimentally popular, being used to try to develop new vaccines for difficult-to-vaccinate-against viruses such as ebolavirus and HIV.
Vi capsular polysaccharide vaccine (ViCPS) against typhoid caused by the Typhi serotype of Salmonella enterica. Instead of being a protein, the Vi antigen is a bacterial capsule polysacchide, made up of a long sugar chain linked to a lipid. 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.
Virus-like particle (VLP) vaccines use VLPs, which are proteins that mimic real virus particles. They generally consist of proteins assembled into the natural shape of the virus' outer shell (capsid).
Advantages and disadvantages
- Cannot revert to virulence meaning they cannot cause the disease they aim to protect against
- Safe for immunocompromised patients
- Can withstand changes in conditions (e.g. temperature, light exposure, humidity)
- Reduced immunogenicity compared to attenuated vaccines
- Can be difficult to isolate the specific antigen(s) which will invoke the necessary immune response
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- "What are protein subunit vaccines and how could they be used against COVID-19?". GAVI. Archived from the original on 2021-08-17.
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