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. The pandemic of coronavirus infection caused by COVID-19 is an urgent problem today. Therefore, the search for optimal and safe ways to prevent the occurrence of this infection or its severe consequences is of great interest to scientists and clinicians worldwide. The most effective way to do this is vaccination, which, unfortunately, in the case of COVID-19, is only effective when the antigenic structure of the circulating virus matches the antigens contained in the vaccine. However, the emergence of new strains, due to the ability of the coronavirus to constantly change, which differ from circulating variants and have pandemic potential, leads to the ineffectiveness of previously proposed vaccines. Therefore, this work aimed to determine the main approaches to creating vaccines and the advantages and disadvantages of vaccination by conducting a bibliographic analysis of modern scientific publications. The main approaches to creating a vaccine against COVID-19 were characterized, in particular: vaccines based on an attenuated virus, inactivated vaccines, vector vaccines, protein vaccines, and vaccines based on nucleic acids. The main advantages and disadvantages of each of the proposed options are described. Considerable attention is paid to the issue of immunological imprinting and antibody-dependent enhancement of infection. A detailed analysis of these phenomena was carried out, and their influence on the effectiveness of various vaccines was described. It was established that the use of DNA and RNA vaccines, provided that the problem of their low immunogenicity in humans is solved, is a real alternative for the future development of medicine in the prevention of infectious diseases. The importance of considering the possibility of complications associated with the phenomena of antigenic imprinting and antibody-dependent enhancement of infection when developing vaccines and carrying out mass vaccinations has been proven. Since the complications underlying these phenomena can appear decades after the previous vaccination or epidemic. In addition, the vaccination itself, carried out without taking them into account, can complicate the epidemic process or cause the development of an epidemic of a closely related virus in those areas where this virus and the one against which the vaccination was carried out circulate at the same time.

The study of the mechanisms of the acute stress, the search for novel ways to increase resistance to it, prevention and treatment of pathological processes caused by stress reactions, remain relevant areas of medical and biological research. The study of the problem of stress is impossible without performing experimental studies using the different stress models. The purpose of the study was to prove the effectiveness of the experimental model of acute immobilization stress simulation in rats by atraumatic cervical fold suspension for 6 hours on the basis of morphological studies of target organs. The study involved 8-10 month old 20 albino male rats, weighing 240-260 g. Group I (control) involved intact animals, which were housed in vivarium standard conditions and were not involved in any experiments or tests. Group II (experimental) involved rats, exposed to acute immobilization stress. The animals were sacrificed by decapitation under intraperitoneal anesthesia. After the chest and abdomen dissection, the internal organs were examined with the removal of target organs: thymus, adrenal glands and stomach. The findings show that immobilization of rats by atraumatic cervical fold suspension for 6 hours causes manifestations of the Selye’s triad of stress: acute involution of the thymus, hypertrophy of the adrenal glands, as well as hyperemia of the gastric mucosa. In animals of the experimental group intact areas were interspersed with hyperemic swollen foci, which gave the mucous membrane a colorful mosaic appearance; numerous polymorphic hemorrhages and single erosions were noted; no ulcers were detected. Visually, the thymus in rats, exposed to immobilization stress was smaller, and no other changes were detected. The mass of the thymus in animals of the experimental group, compared to intact animals, decreased by 44.5% from 306.5 ± 17.62 to 166.8 ± 41.69 mg. The differences between the adrenal glands in rats of the control and experimental groups were in the increase in their weight and size in those animals that were exposed to stress. In the experimental group the enlargement of the adrenal gland from 38.8 ± 4.34 to 65.1 ± 9.13 mg, i.e., by 67.8%, was noted. The present study demonstrates the effectiveness of the experimental model of acute immobilization stress in rats by atraumatic cervical fold suspension for 6 hours, since it causes manifestations of the Selye’s triad of stress: acute involution of the thymus, adrenal hypertrophy, and hyperemia of the gastric mucosa.

The morphological aspects of the restructuring of the structural components of the ileum of rabbits during surgery and suturing of the wound defect with synthetic monofilament thread Vikril are investigated. It was determined that when using this modified thread the course of phases of inflammation and formation of connective tissue scar occurs with the active participation of intraepithelial lymphocytes and cells of the diffuse endocrine system associated with villi of the ileal mucosa during active reaction of resistive and metabolic elements. The main reparative changes of the perivullar zone of the intestinal wall were determined in the mucous membrane due to its thickening due to connective tissue edema, destructive and reparative changes of its own plate and cellular elements, as well as accumulation of significant leukocyte infiltrate in the submucosa. Arterioles as a resistive link, capillaries as an exchange link and venules as a capacitive link of HMCR take an active part in response to the inflammatory process and the formation of connective tissue scar. Arterioles of the mucous and submucosal membranes of the ileum in the area of the wound defect responded by expanding the average diameters in the early stages of the experiment (3-7 days) and up to 30 days corresponded to the control parameters. Capillaries spasmed in the early stages of observation and control values reached up to 21 days. Mucosal venules in the early stages of the experiment expanded, and the submucosal membrane on the contrary narrowed and gained control on the 21st day of the experiment. Morphometric parameters of the average number of columnar epitheliocytes with a border in the composition of the villi of the perivullar zone indicate that the absorption of nutrients from the lumen of the ileum in the area of the wound defect in the early stages of the experiment almost does not occur. It was determined that at the end of the experimental study (30 days of observation) the average number of cellular elements of the diffuse endocrine system of ileal villi was not significantly increased (1.1 times) compared with controls, indicating the tension of local endocrine status and at the end of the experiment. In the implementation of the local inflammatory process in the perivullar zone of the ileum involved not only migrant leukocytes that enter the site of inflammation with blood flow, but also intraepithelial leukocytes, which are actively involved in the implementation of the inflammatory process, and their dynamic increase from 3 to 14 days of observation correspond to the phases of the inflammatory process