The Epidemic Index EPI (R-number, R0, Rt, current reproduction number, reproductive rate, rate of infection, current infection rate, etc.) is a good indicator for the growth of the epidemic before the threshold (R-number=1) and until the total number of cases reaches a certain low level, for exampe 2/3 of the overall number of cases in the wave.

This period will be referred to as stage 1 of the epidemic wave. The main objective of health authorities at this stage is to reduce the R-number/EPI to be well below the threshold.

However, at the next stage, stage 2, the R-number may give a wrong impression about the epidemic behaviour. And to reflect the different pandemic behaviour, we introduce the new index, referred to as Epidemic Risk Index (ERI), which, roughly, estimates the risk of the next wave. As for the traditional R-number, the threshold may be treated as 1, again, that is the ERI numbers above 1 indicate higher risk then it is now, and the ERI numbers below 1 show the smaller risk.

Roughly, reducing the ERI number twice is the same as to decrease twice the potential number of cases in the next epidemic wave. This suggests the following health policy for stage 2: to set up the adequate ERI number above which the higher alert measures apply.

Notation: EPI - Epidemic Index; ERI - Epidemic Risk Index.

The countries in the lists have progressively been chosen to fill in the top 50 states in the new daily cases.

March 2022: the lists have been updated, i.e. some countries have been removed from the lists due to the low number of daily Covid19 cases and/or irregular data reporting in these countries.