Different countries are adopting different strategies to face the Covid-10 pandemic 1 . Monitoring Covid-19 lethality and its variation from country to country is essential for supporting governments in selecting the appropriate decisions. The adoption of correct indicators to monitor the lethality of the infection in the course of the outbreak is therefore a crucial issue. 2, 3 The following terms are used in this work: the infection fatality ratio, IFR, indicates the ratio between the total deaths and total infected patients within a given population; the final case fatality ratio, CFR itself in the course of an outbreak, as better clarified in the following, is a tricky and non-trivial operation. Large and efficient testing programs allow accounting for non-symptomatic patients, thus increasing ccc(t).
This lowers the error (a), i.e. lowers fin CFR to values closer to IFR. This work is instead dedicated to the evaluation of error (b). 
Days from the start of the outbreak
Both the simulation and the examples above clarify that scientists and policymakers should beware of   CFR t as a misleading indicator for calculating the infection fatality rate in the course of the outbreak, even if our attention is only restricted to the subset of confirmed cases. More comprehensive data analysis methods based on the estimate of the average diagnosis-to-death delay time TD are needed. The largely discussed 5 difference in the  
Italy and other major European countries addressed in this work, except for the case of Germany, are rather to be attributed to the more advanced stage of the Italian epidemic. The fin CFR for IT, ES, FR, UK, NL are expected to be grossly comparable at the end of the epidemic, all well above 10%. Germany is converging to lower fin CFR . Probably larger and more efficient testing programs contribute to this result.