Influenza Vaccination and Hospitalizations Among COVID-19 Infected Adults

Introduction: To date, there are no effective treatments for decreasing hospitalizations in Coronavirus disease 2019 (COVID-19) infections. It has been suggested that the influenza vaccine might attenuate the severity of COVID-19.

Methods: This is a retrospective single-centered cohort review of a de-identified database of 2005 patients over the age of 18 within the University of Florida health care system who tested positive for COVID-19. Comorbidities and influenza vaccination status were examined. The primary outcome was severity of disease as reflected by hospitalization and intensive care unit (ICU) admission. Logistic regression was performed to examine the relationship between influenza status and hospitalization.

Results: COVID-19-positive patients who had not received the influenza vaccination within the last year had a 2.44 (95% CI, 1.68, 3.61) greater odds of hospitalization and a 3.29 (95% CI, 1.18, 13.77) greater odds of ICU admission when compared with those who were vaccinated. These results were controlled to account for age, race, gender, hypertension, diabetes, chronic obstructive pulmonary disease, obesity, coronary artery disease, and congestive heart failure.

Discussion: Our analysis suggests that the influenza vaccination is potentially protective of moderate and severe cases of COVID-19 infection. This protective effect holds regardless of comorbidity. The literature points to a potential mechanism via natural killer cell activation. Though our data potentially is limited by its generalizability and our vaccination rate is low, it holds significant relevance given the upcoming influenza season. Not only could simply encouraging influenza vaccination decrease morbidity and mortality from the flu, but it might help flatten the curve of the COVID-19 pandemic as well. We encourage further studies into this finding.