Introduction: Vaccination is considered to be the most important measure to control the pandemic of the new coronavirus infection COVID-19. This article attempts to present the results of vaccination campaign against COVID-19 during a six-months period in the Krasnoyarsk Territory. The aim: To assess the effectiveness of vaccination against COVID-19 infection among adults in the Krasnoyarsk Territory. Methods: We used population-based data from the Federal Register of Infected with COVID-19 on COVID-19 cases in the Krasnoyarsk Territory and the Federal Register of Vaccinated against COVID-19 by July 30, 2021. Differences in mortality, proportions of patients who need in-hospital treatment, proportions of patients in extremely serious and serious conditions, proportions of patients who required artificial ventilation and hospitalization in intensive care between vaccinated and non-vaccinated, as well as immunized and non-immunized COVID-19 patients were calculated. Results: Those who were vaccinated (regardless of the timing of the disease after vaccination) and those who were immunized (42 days after the introduction of the first component of the vaccine) were significantly less likely to suffer from COVID-19 (14.6 patients per 1 000 vaccinated and 16.8 per 1 000 immunized versus 116.9 patients per 1 000 unvaccinated and 112.1 per 1 000 non-immunized, respectively), and in the case of the disease after vaccination, there is a much lighter course of disease with a lower proportion of cases requiring hospitalization (18.3 % versus 24.5 %) or treatment in intensive care units (0.8 % versus 1.6 %), artificial ventilation (0.6 % versus 1.3 %) and low case fatality(2.1 % versus 3.3 %). Conclusion: The study provides the evidence on less severe course of COVID-19 among vaccinated and immunized individuals supporting earlier reports on the effectiveness of vaccination against COVID-19 and in role of mass vaccination in combating COVID-19.