Effective reproduction number

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This map is displaying our crude estimate of the effective reproduction number “Reff”, based on growth data from the past week, assuming a serial interval of 5 days. The number can be thought of as the expected number of infections directly generated by one additional infection. We estimate that the basic reproduction number (or “R”) without any mitigation in most countries is likely somewhere between 2 and 5.
Current values reflect all mitigation measures taken, and also that the fraction of susceptible individuals in the population is gradually decreasing.

The basic interpretation of this number is as follows

  • If R is below 1, the epidemic is shrinking.
  • If R is around and slightly above 1, the epidemic could be either shrinking or growing, but slowly.
  • If R is larger than 2 the the mitigation is insufficient to keep the epidemic under control, and the growth is rapid.

Due to limited resources and data availability, we currently cannot make estimates for every country. If countries are coloured in black, this indicates that we have not estimated case numbers for this country. Note that this does not mean that we have estimated the number of active cases to be zero cases.