History of influenza immunization in COVID-19 patients: impact on mortality.

INTRODUCTION: In the context of the COVID-19 pandemic, there is concern regarding the impact of the influenza season. OBJECTIVE: To analyze the impact of influenza immunization history on patients with SARS-CoV-2 infection. METHODS: Patients older than 18 years with COVID-19, registered between March and August 2020, were included. Data were analyzed using Fisher's exact test and Student's t-test. To evaluate the impact on mortality, a logistic regression model was used; the relationship between the percentage of patients who received the influenza vaccine and mortality was determined with Pearson's correlation coefficient. RESULTS: 16,879 participants were included; 17 % had a history of influenza vaccination. Mortality was lower in the group with a history of vaccination (3.5 % vs. 7 %, p < 0.0001). The vaccination rate had an inverse relationship with the mortality rate (Pearson's r: -0.922, p = 0.026). CONCLUSIONS: Previous influenza immunization was an independent protective factor for mortality in patients with COVID-19. Although further studies are needed to determine a causal relationship, it would be reasonable to increase influenza immunization in the general population.