The purpose of this study is comparison of the duration of progression of the CT picture to a critical degree in various "waves" of the pandemic, the search for factors influencing the interval of "debut diseases - CT 4", as well as the assessment of the state of the lung tissue after a total process in a long period of time.

Materials and methods: a retrospective analysis of 708 patients (226 in the first wave, 482 in the second wave), hospitalized at City Clinical Hospital No. 15 and having a critical degree of lung. 25 discharged patients underwent a control CT scan 6 and 12 months after discharge from the hospital.

Results: The study groups were comparable in terms of demographic characteristics and the degree of CT at admission in hospital. When comparing the interval "onset of the disease - detection of CT-4", no significant differences between the "waves" were found (p = 0.372). When assessing the CT-picture in the delayed period, there were no significant differences in the frequency of changes between the groups; an almost complete regression of inflammatory changes was observed. In the study of the entire sample, an increase in the interval "onset of the disease - detection of CT-4" (p = 0.033) was found in men (11 days (7-16)) compared with women for 10 days (6-15), and in discharged patients (12 days (8-18) compared with deaths (10 days (6-15)) (p <0.001). There was a significant reduction in the progression time with increasing age of patients (p = 0.003)

Conclusions: Considering the data obtained on the possible influence of the timing of the progression of the CT picture on the mortality of patients, as well as the results of long-term observation, it is advisable to search for modifiable risk factors for the rapid progression of the disease.