Effectiveness of influenza vaccination against coronavirus disease (COVID)-19 outcomes in hospitalized individuals in Brazil: an epidemiological study.

Objectives: This study aimed to evaluate the impact of the flu vaccination on the mortality of hospitalized individuals with coronavirus disease (COVID)-19 in Brazil.

Study Design: A retrospective cohort study was conducted based on epidemiological data released by the Brazilian Ministry of Health.

Methods: An observational study was performed using epidemiological data available at OpenDataSUS. The primary outcome was death-the study period comprised December 29, 2019, to April 6, 2023. The odds ratio with a 95% confidence interval (OR; 95% CI) was calculated to evaluate the association between the epidemiological markers, including the vaccination status against influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and the outcome using a multivariable analysis.

Results: The study comprised 791,891 hospitalized individuals with COVID-19. In the study, male sex, older age, living in rural areas, and race (Black and Indigenous peoples), as well as the presence of clinical signs, comorbidities (except the presence of asthma, which was protective), need for intensive care unit, and invasive mechanical ventilation, were associated with a higher chance of death; the vaccination was protective. Among patients with COVID-19, the individuals who received vaccination against influenza [N = 138,564; OR = 0.754 (95% CI = 0.742-0.766)], SARS-CoV-2 [N = 114,628; OR = 0.630 (95% CI = 0.620-0.641)], or both vaccines [N = 55,616; OR = 0.544 (95% CI = 0.531-0.556)], when compared to the individuals who received no vaccination (N = 483,083), had a lower chance of death.

Conclusions: The flu vaccination might be responsible for decreased mortality in hospitalized patients with COVID-19 in Brazil.