Influenza vaccination mitigates severe complications in hospitalized patients: A ten-year observational study, Spain, 2009-2019

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. 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. 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 = .385). 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. •Influenza Vaccination Lowers Complication Risk: Spanish study finds vaccination reduces severe complications in flu patients.•Effective Defense Against Respiratory Issues: Vaccination lowers pneumonia, ARDS, and organ failure risk.•Substantial Decrease in ICU Admissions: Influenza vaccination linked to fewer ICU admissions, easing health care strain.•Strengthening Influenza Prevention Strategies: Research emphasizes enhancing vaccination coverage for maximum effectiveness.•Age and Comorbidities Impact Disease Severity: Advanced age and specific comorbidities contribute to severe influenza cases, requiring tailored prevention.