Comparative analysis of the results of clinical-laboratory and instrumental data from 379 patients hospitalized during 2009—2016, with influenza complicated with pneumonia, showed that the most severe lung lesions were statistically significantly more likely to develop in the first three days caused by shift changed influenza agent in patients with comorbid diseases — chronic diseases of heart and vessels (in isolation or in association with other factors). The differences of the main characteristics of pneumonia and the patterns of cytokine responses between survivors and deceased patients with a severe form of influenza.