The goal we set in our study has had no precedent either in the Hungarian or in the international literature: our intention was to quantify the effectiveness of influenza vaccination based on facts, and to define the number of non-occurred diseases as a result of vaccination. We evaluated data from the influenza season of 2018/2019 in our study. We analyzed the available data on population, vaccination and the number of diseases, and drew objective conclusions therefrom. It was a problem that the basic data appeared in different data sets for different age groups, so we had to find a consensus between them, and establish comparable age groups. Ultimately, we defined three distinct age groups: the age group of minors (0-18 years), the economically active (19-59 years) and the age group of over 60 years. These three age groups became well distinguishable by population, vaccination, and morbidity. We described the influenza disease in general, the characteristics and variability of the influenza virus. We defined the typically affected age group, the number of patients to be treated, the trends for the past 5-10 years. The presented facts, numbers, the results of the calculations, and the conclusions drawn clearly show – excluding subjectivity – the preventive effect and effectiveness of vaccination, which was quantified for the first time in Hungarian literature.