BACKGROUND Our study provides a unique opportunity to compare the course of the disease with a new coronavirus infection in seriously ill patients in the groups of vaccinated and unvaccinated patients hospitalized in the infectious intensive care units of N.V. Sklifosovsky Research Institute for Emergency Medicine of the Moscow Health Department since the start of the vaccination campaign.AIM OF STUDY  The  study of  the  composition  of  hospitalized  patients  with  COVID-19  in  the  N.V. Sklifosovsky Research  Institute  for  Emergency Medicine of the Moscow Health Department in serious condition, requiring resuscitation, in groups of vaccinated and unvaccinated patients in terms of their age and gender characteristics, the severity of the condition and duration of treatment, the presence of concomitant (chronic) diseases, as well as the outcome of hospitalization.MATERIAL AND METHODS The initial analyzed material was data from the Unified Medical Information and Analytical System (EMIAS) of the Institute and statistical cards of patients who left the hospital. The formation of the main group of vaccinated patients was carried out in accordance with the instructions of the Moscow Department of Health and in pursuance of the letter of the Office of Rospotrebnadzor for the city of Moscow No. I-17-17/1 dated January 26, 2021 “On monitoring COVID-19 cases in those vaccinated against a new coronavirus infection “. The Institute has created a registry of hospitalized patients diagnosed with Coronavirus infection caused by the COVID-19 virus, who have a certificate of vaccination with registration in EMIAS. Also, to determine vaccinated patients, we used information from the Headquarters for measures to prevent the importation and spread of infection caused by the 2019-nCoV coronavirus in the city of Moscow. The comparison group included patients with coronavirus infection caused by the SARS-CoV-2 virus, hospitalized in the infectious diseases intensive care units of the Institute and not having information about the certificate in EMIAS. The analyzed period was counted from the moment the register was created and amounted to 6 months: from May 1 to October 31, 2021. Discrete numerical accounting characteristics of each unit of observation (hospitalized patient) were age, duration of stay in the hospital (including in intensive care). Categorical data were gender, diagnosis, source of admission, severity, presence of pneumonia upon admission, history of chronic diseases, outcomes of hospitalization. After the anonymization of the personal data of patients and the distribution of patients into comparison groups, the obtained information was processed by standard means of mathematical statistics using the R-free software computing environment. The calculation of additional absolute and relative values, average errors of indicators was made. Statistical significance of differences in numerical values was determined using the Student’s t-test, categorical values were calculated using the ӽ2 test. In both cases, the p-value was chosen to be less than 0.05.RESULTS When comparing the course of coronavirus infection, concomitant diseases, the duration and nature of inpatient treatment, the frequency of external and internal transfers between different departments, as well as disease outcomes in vaccinated and unvaccinated patients hospitalized at N.V. Sklifosovsky Research Institute for Emergency Medicine of the Moscow Health Department revealed:the average duration of stay both in clinical units and in intensive care units in vaccinated patients is significantly less than in unvaccinated patients;all patients were admitted to the hospital in a serious or extremely serious condition caused by severe clinical manifestations of coronavirus infection in unvaccinated patients and comorbid diseases in most of the vaccinated patients;the mortality among vaccinated patients is significantly lower, and the immediate cause of death was almost always complications of a severe course of competing (non-infectious)CONCLUSION The study showed that in vaccinated patients with intense post-vaccination immunity, the risk of developing a severe course of coronavirus infection (requiring resuscitation) is much lower. Along with this, the duration of treatment is also significantly reduced, especially in intensive care units, and the likelihood of an unfavorable outcome of the disease is reduced to a minimum.