Influenza Vaccination Mitigates Severe Complications in Hospitalized Patients: A Ten-Year Observational Study, Spain, 2009-2019.

Background: Influenza epidemics annually impact a substantial portion of adults worldwide, leading to numerous hospitalizations and fatalities. While the primary goal of vaccination is to prevent influenza virus infection, breakthrough infections can still occur despite vaccination. Evaluating the vaccine effectiveness in preventing severe cases among hospitalized patients is crucial for enhancing vaccination strategies. Methods: This single-center, observational, cross-sectional, and retrospective study analyzed data from 1,357 patients admitted to La Paz University Hospital for influenza infection between 2009 and 2019. Patients' demographics, clinical variables, comorbidities, vaccination status, and influenza-related outcomes were assessed. Logistic regression analysis was performed to determine the vaccine-independent protective effects. Results: Influenza vaccination independently prevented severe complications, including pneumonia, bacterial superinfection, acute respiratory distress syndrome, and multiple organ failure in hospitalized patients (odds ratio = 0.61, 95% confidence interval: 0.47-0.76). Vaccinated patients had significantly lower intensive care unit admission rates (odds ratio = 0.42, 95% confidence interval: 0.18-0.92). However, there were no significant differences in mortality rates between vaccinated and unvaccinated patients (P P = .385). Conclusions: Our study provides robust evidence supporting the influenza vaccine protective effect against severe outcomes in hospitalized patients during epidemic flu. Vaccination is associated with a significant reduction in severe complications and intensive care unit admissions, emphasizing its importance as a preventive measure. Improving vaccination coverage, especially in specific comorbidities and age groups, could further enhance the vaccine effectiveness in preventing severe influenza cases. (c) 2023 Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved.