Live attenuated vaccines (attenuated and non-pathogenic for humans). It takes a very long time to develop them: some developments ended in success only 20 years after the start of work. The fact is that the process of creating them is a trial and error method. Thus, a vaccine against yellow fever was obtained after more than two hundred consecutive processes of transmitting the virus through various animals. Examples of such vaccines: vaccines against smallpox, polio, measles, mumps, rubella, yellow fever and some others. No such drugs have been developed against the current coronavirus.
Inactivated vaccines – in them a live virus is inactivated either chemically (formaldehyde or beta-propiolactone) or by physical methods (heating, ultraviolet irradiation) and purifies very well. Examples: tick-borne encephalitis, hepatitis A, influenza, rabies vaccines. Inactivated vaccines against coronavirus were developed earlier than anyone else in China and India and are already widely used. Although only the first stages of phase 3 clinical trials have been completed. These vaccines are safe and seem to be over 70% effective. In Russia, such a vaccine “KoviVac” was developed at the Federal Research Center for Research and Development of Immunobiological Preparations named after V.I. M.P. Chumakov RAS; Phase 3 clinical trials of this vaccine are underway, the preliminary results of which will be known in May 2021.
Subunit vaccines , consisting of protein – the main antigen of the virus. For this, the protein is either isolated from a viral preparation (split vaccine against influenza), or obtained by a recombinant method. Examples: widely and successfully used vaccines against hepatitis B and papillomavirus. They also try to mimic these proteins with pieces – peptides; there are no successful and widely used drugs in the category of such vaccines; although there have been developments of this type of vaccine against dengue and malaria, they have not been successful. Now the parameters of the candidate peptide-protein vaccine “Epivac-Corona” against the current coronavirus, developed at the State Research Center of Virology and Biotechnology “Vector” of Rospotrebnadzor, are being studied .. But there are no top-rated scientific publications on it yet, and its parameters are still not clear. Therefore, she remains a candidate.
Vector vaccines – the gene of the main immunogenic protein of the target virus is inserted into the genome of a non-pathogenic virus, usually defective in reproduction in the human body, and the resulting recombinant virus is introduced into the body as a vaccine. In this case, such a recombinant virus enters the cells of the body, the matrix RNA of the main immunogenic protein of the target virus is synthesized in the cell on the matrix of its genome, and this very immunogenic protein is synthesized with its use in the cell. Then it is inserted into the cell membrane, mimicking a virus, exposed on it, and an immune response to such an exposed protein is formed. Note that the protein of the viral vector itself is also synthesized, which leads to significant side reactions, but without any long-term consequences. Examples: vaccines against Ebola virus disease based on adenovirus and vesicular stomatitis virus from the American companies Merck, Sharp & Dohme and Johnson & Johnson, which showed a protective effect during trials in Africa during the epidemic in the Democratic Republic of Congo. In Russia, the development of a vector vaccine against coronavirus has advanced the farthest, according to the results of its research, two articles were published in the world famous magazine The Lancet, its protective effect is estimated at 91.6%, and it is allowed for mass use in Russia, the Republic of Belarus, Hungary and some other countries. The vaccine is reactogenic: in about half of people, after the first dose, the temperature rises for 1-2 days, but the protective effect is very good. And no distant consequences have been identified.
Vaccines based on messenger RNAs packaged in lipid nanoparticles work in a similar way, and these lipid vesicles fuse with the cell membrane, releasing mRNA into the cell. And then all processes proceed in the same way as described above for vector vaccines: viral proteins are synthesized on the matrix of these mRNAs, they are inserted into the cell membrane, mimicking the virus, and an immune response is developed to this protein exposed from the membrane. At the same time, the cell does not produce any additional protein products in comparison with vector vaccines. Examples: the current mRNA vaccines against coronavirus by Pfizer and Moderna, recently approved for mass use in some countries, as well as similar drugs being developed in a number of countries, including in Russia: in the Biocad joint-stock company, St. Petersburg, and some others organizations. It is these vaccines that are now leading in the world in terms of the volume of use, although they are very difficult to store and transport: subzero temperatures are required.
The strategically most promising new approaches to vaccine development are vaccine technologies based on mRNA preparations, since they can be used repeatedly. Whereas repeated use of vector vaccines may be ineffective due to the development of immunity to the proteins of the viral vector itself.
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