Viruses use their spikes to attach themselves to human cells during an infection. It exploits the machinery of the host cell to replicate after entering the cell, creating viral proteins and genetic material. As the host cell dies, they are combined into new virus particles and discharged.
Resultantly, more cells are infected by new virus particles, which destroy body tissues and cause symptoms. Infected cells send out warning signals to the immune system by exhibiting viral protein fragments on their surfaces. By doing so, infected cells are believed to transmit the viral antigen to specific immune cells, such as cytotoxic T-cells, and so activate them.
At the same time, detritus from dead cells and virus particles are taken up by so-called professional Antigen-Presenting Cells, the most effective of which are dendritic cells.
Dendritic cells patrol the tissues of the body, constantly sampling their surroundings for intruders. Dendritic cells swiftly leave the tissue after capturing the antigen and travel to the next lymph node, where they present the antigen to another type of immune cell known as helper T-cells. B-cells in lymph nodes are also activated by viral particles.
These immune cell clusters collaborate to mount two types of antiviral immunity:
- Cell-mediated immunity
- Antibody-mediated immunity
However, the procedure could take many weeks, during which time the person will be sick and the virus will have damaged a large number of cells.
Vaccines give viral antigens to the immune system without inducing disease. A vaccine-generated immune response is comparable to that induced by a natural infection, albeit some vaccinations may only induce antibody-mediated immunity, making them less effective. Even when there is no infection, the immune system can produce symptoms that resemble a mild infection. For a few days, the lymph nodes near the injection site may become swollen and sore as they begin to produce antibodies. This is proof that the vaccine is working against infection.
Many existing vaccinations contain a virus that has been attenuated or inactivated. Because the entire virus is used in these vaccines, significant safety testing is required. In those with weakened immune systems, attenuated vaccinations may still cause sickness.
- Only antibody-mediated immunity is induced by inactivated vaccines (Sinovac, Covaxin).
- Only a portion of the virus, usually a spike protein, is contained in subunit vaccinations (EpiVacCorona).
Although these vaccinations do not cause disease, they may not be seen as a danger by the immune system and hence fail to elicit the desired immunological response.
As a result, adjuvants are frequently used to encourage antigen-presenting cells to recognize the vaccine. A subunit vaccination could alternatively be made out of empty viral shells that haven't been genetically modified. These vaccines may not require adjuvants to be seen as dangerous because they have the size and structure of a disease, but they are difficult to make.
Instead of the antigen itself, nucleic acid vaccinations contain genetic instructions for generating the viral antigen. Viral DNA is introduced into the nucleus of the cell, where it is translated into mRNA. In the cytoplasm, mRNA is translated into viral spike protein. Like other types of vaccines, the protein is then exhibited on the cell surface.
To reach the cell's nucleus, naked DNA vaccines (Inovio) require a specific delivery technique. Alternatively, a virus that isn't related to the DNA could be utilised to distribute it. The vaccine is also known as a viral-vector vaccine (Sputnik V; Johnson & Johnson's) in this situation.
The Oxford-AstraZeneca Covid-19 vaccine, for example, uses a chimpanzee's adenovirus as a vector. The coronavirus spike gene is inserted to the adenoviral genome, which has been edited to eliminate viral genes. The viral vector cannot reproduce or cause disease in this manner, but it does serve as a vehicle for delivering the DNA. Because most people have been exposed to human adenovirus and have developed immunity to it, a non-human adenovirus is employed. Immunity may kill the vehicle before the DNA can be delivered, reducing the vaccine's effectiveness.
Concerns about viral DNA integration into the human genome have arisen as a result of DNA vaccinations. However, research in animal models have revealed that the incidence of integration is far lower than that of natural, spontaneous gene changes.
mRNA vaccines (Pfizer, Moderna) deliver mRNA, which provides the instructions for producing the viral protein. mRNA molecules are transported in a lipid coating that will merge with the cell membrane when it reaches it. The mRNA is translated into viral antigen in the cytoplasm and subsequently presented on the cell surface. mRNA vaccines, unlike DNA vaccinations, are highly unlikely to incorporate into the human genome.
Apart from all of the information we have so far, we are unable to compare any vaccine to another at this time. Because there is still a lot of research to be done on this subject.
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