Effective reproduction number estimation from data series

The COVID-19 pandemic spreading determined the need for several countries to define methods to show the current status of the spreading in each country, in each region or even in each municipality. During the initial expansion phase, it was important to establish which was the growth rate and after the introduction of containment measures to provide a method to understand the effectiveness of the implemented measures. In the current phase of de-escalation there is a great interest in understanding when it is necessary to reintroduce containment measures on the basis of the possibility of resurgence of the spread. The objective of this Technical Note is to consider a selection of these methods to highlight merits and issues and apply them for a number of actual cases.