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Relevance. The new coronavirus infection (COVID-19) is still a public health problem and a threat to socio-economic well-being. Most studies have focused predominantly on humoral immunity, and there are no data on the cellular composition of blood in dynamics. Aim. To study the dynamics of changes in blood cellular composition depending on the type of immunity formed (natural, hybrid, breakthrough, postvaccinal) to SARS-CoV-2 virus. Materials and Methods. A total of 130 volunteers participated in the study. Immunophenotyping of peripheral blood leukocytes using flow cytometry was performed. The presence of specific IgG antibodies to N-protein SARS-CoV-2, total IgA and cytokines (IL-4, IL-10, IFN-γ, TNF-α) was assessed in serum by ELISA. Results and Discussion. A statistically significant increase in BL was recorded in volunteers with hybrid immunity 1 month (14,0% (12,3–16,4%)) after vaccination compared to healthy volunteers (9,1% (6,4–10,2%), p = 0,0007) and people with primary COVID-19 infection (10,2% (8,3–12,1%), p = 0,0134). In volunteers with natural and hybrid immunity, as well as in revaccinated people, an increase in B1-cells (CD3-CD19+CD5+CD27-) was observed during 3–9 months of observation. It is shown that the increase of B-lymphocytes with «switched» class of synthesized antibodies was detected in people with breakthrough immunity. Increased levels of T-lymphocytes expressing HLA-DR were recorded in all individuals during 6–9 months of follow-up. Volunteers with breakthrough immunity showed a significant increase in the positivity index when assessing the presence of specific IgG class antibodies to the coronavirus N-protein compared with volunteers with natural and hybrid immunity. Conclusions. Vaccination promotes protective immunity sufficient for timely activation of memory T- and B-cells in breakthrough immunity and maintenance of immunologic efficacy in hybrid immunity against COVID-19. The results help to assess the strain of innate and adaptive immunity in novel coronavirus infection and to fill gaps in the understanding of immunopathogenesis in COVID-19.

Relevance. COVID-19 is accompanied by high production of cytokines - immune molecules, imbalanced regulation of which leads to disruption of the immune response. Therefore, the study of cytokine status in both vaccinated and re-vaccinated patients is necessary to develop an immunoprophylaxis strategy for COVID-19. Aim. To evaluate the cytokine status in COVID-19 survivors and vaccinated employees of a health care facility against this disease. Materials and Methods. Production levels of cytokines (IL-4, IL-10, IFN-γ and TNF-α) were determined by quantitative enzyme immunoassay in serum of 144 volunteers. Results and discussion. A significant 1.5-fold increase in IL-10 and 2.0-fold increase in TNF-α was found in the group of re-invaccinated overinfected volunteers, and a 2.0-fold decrease in IL-4 compared with the vaccinated group. An inverse correlation between IL-4 and IFN-γ levels and timing after the disease was detected. A significant decrease in IL-4 in survivors (Omicron variant) and an increase in IL-10 in the survivors at the beginning of the pandemic as compared to other re-vaccinees was established. In the vaccinated group, regardless of the vaccine used, IL-10 and TNF-α decreased significantly after revaccination. No statistically significant differences were found between the cytokine status parameters in the survivors before and after vaccination. The predominance of the cellular component of immunity was established in all the examined groups, and the highest proportion of persons with a humoral immune response was detected among the vaccinated volunteers, while the highest proportion of persons with a mixed immune response was detected among the overexperienced non-vaccinated patients. Conclusions. The results obtained supplement the available data on coronavirus infection and indicate the need for further research.