Fast COVID-19 vaccine effectiveness estimation on the basis of recovered individual propensity to be vaccinated

Since March 2020, the study of COVID-19 pandemic contagion data has been perceived as relevant by a wide audience composed not only of epidemiologists and specialized personnel but also of press offices, independent agencies, and ordinary people. There is therefore a strong need to provide clear information understandable to a wide unspecialized public. Vaccine efficacy, in terms of risk reducing of infection/hospitalization/ death, is usually estimated by the Government Centers for Disease Control (CDC) through multivariate analysis (e.g. 1,2); however, these statistical methods are often incomprehensible to the general public. To provide immediate information to the general (unqualified) public, the CDCs of different nations (e.g. 3e5), as well as several prestigious press offices (e.g. 6), have published epidemiological data and statistics on dedicated Web pages and dashboards. The main purpose of this article is to point out to the CDCs of the various governments, as well as to independent agencies and press offices, the need and advantages of correcting incidence data of the infection, as well as to propose a practical equation to calculate vaccine effectiveness, based on the count of recovered subjects who have not yet been vaccinated. This equation can be used to accompany data on infection incidence aimed at the general public, as well as an “easy-to-access” formula to be used for the official and institutional communication of the CDCs.