The effectiveness of Influenza vaccination in general Greek population

Introduction: The effectiveness of Influenza vaccines depends on several factors. Comparison of vaccinated with unvaccinated adults show outcome measures and provide the most robust evidence of vaccine efficacy. Aim: To assess the effectiveness of Influenza vaccination in general Greek population and identify specific patient traits of those vaccinated against Influenza (2019-2020) that yet sustained laboratory confirmed disease.Materials and Methods: Retrospective study of all laboratory confirmed Influenza cases in a tertiary national referral centre (12/2019-01/2020), review of patient records (vaccination history 2019-2020, epidemiological data, clinical & laboratory parameters, hospital admission, morbidity and mortality). Results: 400 patients were tested for Influenza, 98 were found positive (Influenza A 93.7%, B 6.3%). 49.5% females, mean patient age 55 years (18-93y). 32.6% of patients had a flu vaccine and yet sustained Influenza. All were immunocompetent and none had any history of active/previous TB. 74% of vaccinated patients with confirmed Influenza required an emergency hospital admission and 13% of those required Intensive Care Unit admission. Mortality on vaccinated patients admitted to hospital was 9.2% and overall mortality for inpatients regardless of vaccination status was 12.5%. Medical personnel compliance with Influenza Incidence form was only 16%. Conclusions: Effectiveness of Influenza vaccination in our sample seems limited. Further investigation is needed as this could pose a significant public health issue.We will expand our research for the entire Influenza season to identify underlying factors to inform public health policies and change clinical practice