COVID-19 and smoking in Russia: how are hospitalizations, course, and outcomes of coronavirus infection related to tobacco use?

Aim . To study the relationship between the level of hospitalizations, se­vere course, and mortality from coronavirus disease 2019 (COVID-19) with the smoking prevalence in Russia for 2020-2021. Material and methods . The article analyzes data on the number of peop­le hospitalized with COVID-19, transferred to the intensive care unit (ICU), and died from COVID-19 in 2020-2021 by age and sex groups in 85 Russian regions from the Federal COVID-19 Registry, as well as data on smoking status, socio-­demographic characteristics of the sample for 2020-2021 in 85 Russian regions from the Sample Monitoring of the Po­pulation Health sample of the Federal State Statistics Service for the cor­responding years. Relationships between the smoking and COVID-19 and severe COVID-19 hospitalization rates with transfer to the ICU and the COVID-19 mortality rate by age and sex groups and federal districts of Russia were analyzed. The assessment was carried out using second-­order polynomial regression (quadratic regression). The model quality was determined based on the coefficient of determination (R 2 ) and the F-cri­terion for the general model. Results . Nonlinear relationships between the studied parameters with a characteristic parabolic dependence were obtained. A significant relationship was found between the prevalence of smoking and the level of severe COVID-19 among men in the age groups of 20-29 years, 50-59 years, 70-79 years (p<0,05). A relationship was found between COVID-19 mortality and smoking rate in men aged 15-19 years (R 2 =0,15, p=0,049), more significant in women (R 2 =0,35, p=0,002); in women aged 30-39 years (R 2 =0,06, p=0,007); in men and women aged 40-49 years and 50-59 with a more pronounced trend; in men aged 60-69 (R 2 =0,05, p=0,018) and in women as a trend (R 2 =0,03, p=0,078); in women aged 70-79 and ≥80 years (R 2 =0,06, p=0,039) with a more pronounced trend in men. Positive associations were found between smoking prevalence and the rate of hospitalization for COVID-19 (R 2 =0,52, p<0,001) and severe COVID-19 (p=0,011) in the Far Eastern Federal District among men, as well as in the Siberian Federal District (p=0,007) and the Ural Federal District. The relationships between the mortality rate from COVID-19 and smoking frequency in different federal districts demonstrate an inverse parabolic dependence. Conclusion . The relationships between smoking and COVID-19 ra­tes are complex and nonlinear. A deep segmented analysis of these rela­tionships revealed significant associations explaining the contribution of smo­king to the rate of hospitalizations and severe outcomes, mortality from COVID-19 in certain age groups of men and women and in various fede­ral districts of Russia. Effective tobacco control measures aimed at reducing smoking are necessary to mitigate the adverse effects of coronavirus infections.