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Subunit vaccine

A subunit vaccine is a vaccine that contains purified parts of the pathogen that are antigenic, or necessary to elicit a protective immune response.[1][2] Subunit vaccine can be made from dissembled viral particles in cell culture or recombinant DNA expression,[3] in which case it is a recombinant subunit vaccine.

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[1][2] or peptides.[4] 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 vaccines containing whole pathogens.[1] Other advantages include being well-established technology and being suitable for immunocompromised individuals.[2] Disadvantages include being relatively complex to manufacture compared to some vaccines, possibly requiring adjuvants and booster shots, and requiring time to examine which antigenic combinations may work best.[2]


The first recombinant subunit vaccine was produced in the mid-1980s to protect people from Hepatitis B. Other recombinant subunit vaccines licensed include Engerix-B (hepatitis B), Gardasil 9[5] (Human Papillomavirus), Flublok[6](influenza), Shingrix[7] (Herpes zoster) and Nuvaxovid[8] (Coronavirus disease 2019).


After injection, antigens trigger the production of antigen-specific antibodies, which are responsible for recognising and neutralising foreign substances. Basic components of recombinant subunit vaccines include recombinant subunits, adjuvants and carriers. Additionally, recombinant subunit vaccines are popular candidates for the development of vaccines against infectious diseases (e.g. tuberculosis,[9] dengue[10])


Recombinant subunit vaccines are considered to be safe for injection. The chances of adverse effects vary depending on the specific type of vaccine being administered. Minor side effects include injection site pain, fever, and fatigue, and serious adverse effects consist of anaphylaxis and potentially fatal allergic reaction. The contraindications are also vaccine-specific; they are generally not recommended for people with the previous history of anaphylaxis to any component of the vaccines. Advice from medical professionals should be sought before receiving any vaccination.

Discovery[edit]

The first certified subunit vaccine by clinical trials on humans is the hepatitis B vaccine, containing the surface antigens of the hepatitis B virus itself from infected patients and adjusted by newly developed technology aiming to enhance the vaccine safety and eliminate possible contamination through individuals plasma.[11]

Mechanism[edit]

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.[2] An effective vaccine would elicit the immune response to the antigens and form immunological memory that allows quick recognition of the pathogens and quick response to future infections.[1]


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 may be weaker. Another drawback is that the antigens do not infect cells, so the immune response to the subunit vaccines may only be antibody-mediated, not cell-mediated, and as a result, is weaker than those elicited by other types of vaccines. To increase immune response, adjuvants may be used with the subunit vaccines, or booster doses may be required.[2]

They contain clearly identified compositions which greatly reduces the possibility of presence of undesired materials within the .[30]

vaccine

Their pathogenicities are minimized as only fragments of the pathogen are present in the which cannot invade and multiply within the human body.[31]

vaccine

They have better [32] and are suitable to be administered to immunocompromised patients.[33]

safety profiles

They are suitable for due to the use of recombinant technologies.[30]

mass production

They have high stability so they can withstand environmental changes and are more convenient to be used in community settings.

[31]

When compared with conventional attenuated vaccines and inactivated vaccines, recombinant subunit vaccines have the following special characteristics:


However, there are also some drawbacks regarding recombinant subunit vaccines:

Cannot revert to meaning they cannot cause the disease they aim to protect against[65][66]

virulence

Safe for patients[67]

immunocompromised

Can withstand changes in conditions (e.g. temperature, light exposure, humidity)

[65]

Adverse effects and contraindications[edit]

Recombinant subunit vaccines are safe for administration.[68][69] However, mild local reactions, including induration and swelling of the injection site, along with fever, fatigue and headache may be encountered after vaccination.[68][70][71] Occurrence of severe hypersensitivity reactions and anaphylaxis is rare,[72] but can possibly lead to deaths of individuals. Adverse effects can vary among populations depending on their physical health condition, age, gender and genetic predisposition.[73][74]


Recombinant subunit vaccines are contraindicated to people who have experienced allergic reactions and anaphylaxis to antigens or other components of the vaccines previously.[75][76] Furthermore, precautions should be taken when administering vaccines to people who are in diseased state and during pregnancy,[75] in which their injections should be delayed until their conditions become stable and after childbirth respectively.

History[edit]

While the practice of immunisation can be traced back to the 12th century, in which ancient Chinese at that time employed the technique of variolation to confer immunity to smallpox infection, the modern era of vaccination has a short history of around 200 years. It began with the invention of a vaccine by Edward Jenner in 1798 to eradicate smallpox by injecting relatively weaker cowpox virus into the human body.


The middle of the 20th century marked the golden age of vaccine science. Rapid technological advancements during this period of time enabled scientists to cultivate cell culture under controlled environments in laboratories,[88] subsequently giving rise to the production of vaccines against poliomyelitis, measles and various communicable diseases. Conjugated vaccines were also developed using immunologic markers including capsular polysaccharide and proteins.[88] Creation of products targeting common illnesses successfully lowered infection-related mortality and reduced public healthcare burden.


Emergence of genetic engineering techniques revolutionised the creation of vaccines. By the end of the 20th century, researchers had the ability to create recombinant vaccines apart from traditional whole-cell vaccine, for instance Hepatitis B vaccine, which uses the viral antigens to initiate immune responses.[88]


As the manufacturing methods continue to evolve, vaccines with more complex constitutions will inevitably be generated in the future to extend their therapeutic applications to both infectious and non-infectious diseases, in order to safeguard the health of more people.