The Relationship of COVID-19 Morbidity and Mortality with the History of Influenza Vaccination

Background: COVID-19 is currently the leading global health issue. Low- and middle-income countries (LMICs) face challenges in supplying COVID-19 vaccines. To assess an adjunctive preventive measure for COVID-19 burden, we aimed to evaluate the relationship of influenza vaccination in the previous year with outcomes of COVID-19 in affirmed cases after adjustment for relevant factors. Methods: This prospective study was conducted using the provincial registry of confirmed COVID-19 cases in East-Azerbaijan province in North-West of Iran. The main outcomes were COVID-19 mortality and hospitalization. The influenza vaccination history in 2019 was collected by phone calls. Data analysis was done by SPSS software version 16, separately for healthcare workers and the general population. The logistic regression model was applied to compare the covariates in influenza vaccinated versus unvaccinated patients. Results: From 1 March to 10 October 2020, 17,213 positive COVID-19 cases were registered, of which 916 patients were included. A total of 88 patients (9.6%) deceased due to COVID-19. Two hundred subjects (21.8%) reported receiving the influenza vaccine during the past year. Healthcare workers had a significantly higher vaccination rate than the general population (28.9% vs. 7.1%; p<0.001). After adjustment for socioeconomic and health covariates, the vaccinated cases in the general population had 84% lower odds of death (OR: 0.16; 95%CI: 0.05-0.60; p=0.017). In multivariate analysis, the influenza vaccination history in the previous year was not significantly related to the lower COVID-19 hospitalization rate. Conclusion: The flu vaccination rate was not optimal in our community. The flu vaccination can be an independent preventing factor for COVID-19 mortality in the general population. The influenza vaccine can be considered as an effective adjutant preventive countermeasure for the COVID-19 burden.