Subunit vaccine
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).
[11] 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.
[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.
The purpose of increasing the vaccine's surface similarity to a whole virus particle (but not its ability to spread) is to trigger a stronger immune response.
Vi capsular polysaccharide vaccine (ViCPS) against typhoid caused by the Typhi serotype of Salmonella enterica.
[23] Instead of being a protein, the Vi antigen is a bacterial capsule polysacchide, made up of a long sugar chain linked to a lipid.
[44] To be immunogenic, they should be of foreign nature and of sufficient complexity for the reaction between different components of the immune system and the candidates to occur.
[50] Notably, yeast incorporates more mannose molecules during N-glycosylation when compared with other eukaryotes,[51] which may trigger cellular conformational stress responses.
Such responses may result in failure in reaching native protein conformation, implying potential reduction of serum half-life and immunogenicity.
[48] Regarding application, both the hepatitis B virus surface antigen (HBsAg) and the virus-like particles (VLPs) of the major capsid protein L1 of human papillomavirus type 6, 11, 16, 18 are produced by Saccharomyces cerevisiae.
[citation needed] Mammalian cells are well known for their ability to perform therapeutically essential post-translational modifications and express properly folded, glycosylated and functionally active proteins.
[49][52][53] However, efficacy of mammalian cells may be limited by epigenetic gene silencing and aggresome formation (recombinant protein aggregation).
[48] The most prominent example under this class is Chinese Hamster Ovary (CHO) cells utilised for the synthesis of recombinant varicella zoster virus surface glycoprotein (gE) antigen for SHINGRIX.
[58][59][60][61] Addition of adjuvants may confer benefits including dose sparing and stabilisation of final vaccine formulation.
[63] Subunits may either be inserted within the carrier or genetically engineered to be expressed on the surface of the vectors for efficient presentation to the mucosal immune system.
[67][68] However, mild local reactions, including induration and swelling of the injection site, along with fever, fatigue and headache may be encountered after vaccination.
Adverse effects can vary among populations depending on their physical health condition, age, gender and genetic predisposition.
[74][75] Furthermore, precautions should be taken when administering vaccines to people who are in diseased state and during pregnancy,[74] in which their injections should be delayed until their conditions become stable and after childbirth respectively.
[7] Systematic reviews and meta-analyses have been conducted on the efficacy, effectiveness and safety of SHINGRIX in immunocompromised 18–49 year old patients and healthy adults aged 50 and over.
These studies reported humoral and cell-mediated immunity rate ranged between 65.4 and 96.2% and 50.0–93.0% while efficacy in patients (18–49 yo) with haematological malignancies was estimated at 87.2% (95%CI, 44.3–98.6%) up to 13 months post-vaccination with an acceptable safety profile.
[8] 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,[citation needed] 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.
[citation needed] Rapid technological advancements during this period of time enabled scientists to cultivate cell culture under controlled environments in laboratories,[87] subsequently giving rise to the production of vaccines against poliomyelitis, measles and various communicable diseases.
[87] Creation of products targeting common illnesses successfully lowered infection-related mortality and reduced public healthcare burden.
[87] 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,[citation needed] in order to safeguard the health of more people.
Recombinant subunit vaccines are used in development for tuberculosis,[9] dengue fever,[10] soil-transmitted helminths,[88] feline leukaemia[89] and COVID-19.
[90] Subunit vaccines are not only considered effective for SARS-COV-2, but also as candidates for evolving immunizations against malaria, tetanus, salmonella enterica, and other diseases.
[11] Research has been conducted to explore the possibility of developing a heterologous SARS-CoV receptor-binding domain (RBD) recombinant protein as a human vaccine against COVID-19.
