What are vaccines?
Vaccines are classified into several categories, however they all act on the same premise. This is done to prime the immune system to recognise a pathogen (a disease-causing organism) or a component of a pathogen. If the immune system is educated to recognise this, the pathogen will be expelled from the body if it is subsequently exposed to it. The immune system recognises foreign ‘antigens,’ which are pathogen elements on the surface or inside the pathogen that are not ordinarily found in the body. To create protection, the earliest human vaccines against viruses used weakened or attenuated viruses. Cowpox was included in the smallpox vaccine because it was similar enough to smallpox to protect against it but did not generally cause major sickness. Rabies was the first virus to be attenuated in a lab and used to develop a vaccine for people.
Types of vaccines
Whole virus vaccines
1) Viral Vectored Vaccines
Unlike most traditional vaccinations, viral vector-based vaccines do not include antigens but instead employ the body’s own cells to manufacture them. They accomplish this by delivering genetic code for antigen, in this case COVID-19 spike proteins present on the virus’s surface, into human cells via a modified virus (the vector). The vaccine simulates what happens during natural infection with some pathogens, particularly viruses, by infecting cells and commanding them to produce huge amounts of antigen, which then triggers an immune response. This has the benefit of inducing a significant cellular immunological response by T cells as well as antibody production by B cells. The rVSV-ZEBOV vaccine against Ebola is an example of a viral vector vaccine.
ADVANTAGES
- Technology that is well-established
- A powerful immunological reaction
- B and T cells are involved in the immune response.
DISADVANTAGES
- Prior exposure to the vector may limit its efficacy.
- Manufacturing is rather difficult.
- Replicating
When utilised as a vaccine delivery platform, replicating viral vectors maintain the potential to generate new viral particles in addition to delivering the vaccination antigen. As with live attenuated entire pathogen vaccinations, this has the natural benefit of providing a continuous source of vaccine antigen over a prolonged length of time compared to non-replicating vaccines, and hence is likely to induce a higher immune response. A single vaccination may be sufficient to provide protection. Replicating viral vectors are often chosen such that the viruses themselves are innocuous or attenuated, so that they cannot cause illness while infecting the host
Non-replicating
During the process of delivering the vaccination antigen to the cell, non-replicating viral vectors lose their ability to generate new viral particles. This is due to the removal of crucial viral gene that allow the virus to proliferate in the lab. This has the advantage of preventing illness and reducing unpleasant outcomes associated with viral vector proliferation. However, vaccine antigen can only be generated when the first vaccination is still present in infected cells (a few days).
VACCINE which used viral vector technique: astra Zeneca and johnson and johnson
2) inactivated Vaccine
The first step in creating a vaccine is to inactivate or kill the disease-carrying virus or bacteria, or one that is substantially similar to it, using chemicals, heat, or radiation. This strategy employs technology that has been shown to be effective in humans – this is how flu and polio vaccinations are produced – and vaccines can be produced on a reasonable scale. However, it takes sophisticated laboratory equipment to safely cultivate the virus or bacteria, can take a relatively lengthy time to produce, and will almost certainly require two or three doses to be delivered.
example is India’s covaxin
3) Vaccine with live attenuation
A live-attenuated vaccine employs an alive but weakened form of the virus, or one that is extremely close to it. This type of vaccination includes the (MMR) vaccine as well as the chickenpox and shingles vaccine. This method, like the inactivated vaccine, employs comparable technology and can be produced on a large scale. However, such vaccinations may not be appropriate for those with impaired immune systems.
4) Subunit vaccines
Subunit vaccines include purified fragments of a pathogen that have been particularly chosen for their capacity to activate immune cells rather than injecting the entire pathogen to elicit an immune response. Subunit vaccinations are regarded extremely safe since these pieces are incapable of producing illness.
There are various varieties: Polysaccharide vaccines comprise sequences of sugar molecules present in the cell walls of some bacteria; conjugate subunit vaccines attach a polysaccharide chain to a carrier protein to try to increase the immune response. Other subunit vaccinations are already being used widely. The hepatitis B and acellular pertussis vaccines, the pneumococcal polysaccharide vaccine, and the MenACWY vaccine (polysaccharides are examples
Vaccines based on Recombinant Proteins
Recombinant vaccines are created by employing bacterial or yeast cells to produce the vaccine. A little bit of DNA from the virus or bacteria that we wish to preserve is extracted and put into the producing cells. To manufacture the hepatitis B vaccine, for example, a portion of the hepatitis B virus’s DNA is incorporated into the DNA of yeast cells. These yeast cells may then manufacture one of the hepatitis B virus’s surface proteins, which is purified and utilised as the active element in the vaccine. These polysaccharides or proteins are known as antigens because they are recognised as ‘foreign’ by our immune system.
Even if the vaccine only contains a few of the thousands of proteins found in a bacteria, they are sufficient to elicit an immune response that can protect against the disease.
Toxoid vaccines
When some bacteria assault the body, they release toxins (poisonous proteins), and it is the toxins, not the germs, that we wish to be protected against. The immune system recognises these toxins in the same way that it recognises other antigens on the bacteria’s surface and can develop an immunological response to them. Inactivated forms of these toxins are used in several vaccinations. Toxoids are so-called because they resemble toxins but are not harmful. They elicit a powerful immunological response.
vaccines which use protein subunits are novovax
ADVANTAGES
- Technology that is well-established
- Appropriate for persons with weakened immune system
- no living components, there is no possibility of the vaccination causing illness.
- stable
DISADVANTAGES
- Manufacturing is rather difficult.
- It is possible that adjuvants and booster injections will be necessary.
- It takes time to find the ideal antigen mix.
5) Nucleic acid vaccines
Nucleic acid vaccines employ genetic material from a pathogen, such as a virus or bacteria, to induce an immune response against it. Depending on the vaccination, the genetic material might be DNA or RNA; in all cases, it offers instructions for producing a specific pathogen protein that the immune system will recognize as alien (an antigen). When this genetic information is injected into host cells, it is read by the cell’s own protein-making machinery and utilised to produce antigens, which subsequently activate an immune response.
ADVANTAGES
- immune response involves B cells and T cells
- No live components, so no risk of the vaccine triggering disease
- Relatively easy to manufacture
DISADVANTAGES
- Some RNA vaccines require ultra-cold storage
- Never been licensed in humans
- Booster shots may be required
RNA vaccines
mRNA (messenger RNA) is used inside a lipid (fat) membrane in RNA vaccinations. This fatty coating both protects the mRNA when it initially enters the body and assists it in entering cells by bonding with the cell membrane. Once within the cell, machinery inside the cell converts the mRNA into the antigen protein. This mRNA normally lasts a few days, but enough antigen is produced during that period to induce an immunological response. The body then naturally breaks it down and eliminates it. RNA vaccines do not have the ability to combine with the human genetic code (DNA).
RNA vaccines are used in both the Pfizer BioNTech and the Moderna .
DNA vaccines
Because DNA is more stable than mRNA, it does not require the same level of protection at the start. DNA vaccines are often delivered via an electroporation approach. This method employs low-level electrical waves to allow the DNA vaccination to be absorbed by the body’s cells. Before DNA can be translated into protein antigens that elicit an immune response, it must first be translated to mRNA within the cell nucleus. There are presently no licenced DNA vaccines, although many are in the works.
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