EPIDEMIOLOGICAL COMPARISON OF INFLUENZA, ARI AND COVID-19 PREVALENCE IN BULGARIA FOR THE PERIOD 2017-2022

Introduction: The report presents a comparison of the incidence of respiratory infections - influenza, other acute respiratory infections and COVID-19 for the period 2017-2022. A comparative analysis of the epidemiological dynamics in different areas of the country is made and factors such as demography and vaccine coverage are also analyzed. Materials and Methods: A comparative analysis of the prevalence of Influenza/ARI, and COVID-19 was made for the years of the studied period. Regional values were compared to the country total in order to rank regions according to the experienced disease incidence burden at a regional level. The percentile method was used to identify and filter the regions where Influenza/ARI waves appeared with the highest intensity in the country. To compare intensity of COVID-19 waves between the selected regions we used the maximal weekly incidence values per 100 000 population reached for the different periods of the pandemic. Information on the age structure of the population in the respective regions and the vaccine uptake was retrieved and compared. Results: The regions of Blagoevgrad, Montana, Haskovo, Razgrad, Kardzhali, Sliven and Targovishte were filtered among all regions as the ones with the most intensive Influenza waves for the period 2017-2022.  Blagoevgrad and Sliven were the regions with higher maximal COVID-19 incidence values before the Delta circulation and during the Omicron predominance. When the Delta variant was predominant, Blagoevgrad and Montana surpassed the incidence recorded for the country. No data supporting the initial hypothesis that demographic structure at regional level determines intensity of spread of the two viral respiratory infections was found. However, the regions with higher COVID-19 vaccines coverage were found to have the lowest incidence levels of the infection. Conclusion: Although COVID-19 and Influenza/ARI are both respiratory infections, they differ in their epidemiology and no specific pattern can be found. We recommend that anti-epidemic measures should be followed to limit incidence regardless of the circulating respiratory pathogen.