Do repeated vaccinations affect the incidence of coronavirus infection?

Coronavirus infection caused by the SARS-CoV-2 virus is becoming one of the seasonal respiratory infections, which requires a decision on the continuation of vaccination for certain groups of people.
The purpose: To study the relationship between the clinical and immunological efficacy of vaccination and revaccination against COVID-19 in people of different ages, health conditions and occupational risk.
Research methods: Clinical observation of 258 adults who were vaccinated and revaccinated, as well as those with hybrid immunity, in a catamnesis for 2 years after vaccination with an assessment of the frequency and severity of confirmed coronavirus infection; laboratory examination of antibody titers (IgG to RBD fragment of S – protein) in blood serum over time by enzyme immunoassay; statistical data processing.
Results: The average antibody levels after vaccination were 353.1±35.9 BAU/ml, after the first revaccination 481.6±30.1 BAU/ml, and 2471.1±811.9 BAU/ml after the second revaccination (p<0.01 Student’s criterion). In individuals with hybrid immunity, after vaccination, 424.7±15.9 BAU/ml, after revaccination, 457±99.9 BAU/ml, respectively. The incidence among those vaccinated was 32.9% after primary vaccination and 21.9% after revaccination. The level of antibodies before the disease in patients was significantly lower than in those who did not get sick (pt<0.005). After revaccination, there were no significant differences in the level of antibodies before the disease in those who were ill and those who were not. Among people with hybrid immunity, 27.1% became ill after vaccination, also without significant differences in antibody levels before the disease in those who were ill and those who were not. Medical workers were significantly less likely to get sick than non-medical workers (16.7% and 66.7%, p<0.05). A relatively strong correlation (Pearson coefficient) of disease risk was confirmed, despite the presence of revaccination, in people over 60 years of age, compared with the young (k=0.418) and middle (k=0.432) age groups.
Conclusion: People with hybrid immunity have the same patterns in disease prevention as vaccinated and revaccinated people. The age over 60 determines the need for routine revaccinations. Medical workers are not at increased risk of infection if they have been vaccinated, revaccinated, or have developed hybrid immunity.

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