Countries with the best covid-19 control: half-lives of 5 days

The first chart shows the new cases reported in seven countries that have done well in controlling their covid-19 outbreaks - they have all reduced the rate to less than 5% of the peak rate (the percentage shown against each country is the latest rate as a percentage of the peak rate).

South Korea and China have had some secondary spikes, but appear to be dealing with them well. (The y-axis is logarithmic.)

By eye, there appears to be a similar decline in rates in many of the countries: the declines are approximately straight line, and the slopes of decline are approximately parallel. As the y-axis scale is logarithmic, this means that the declines are approximately exponential, with a similar half life. Measurement of the slope of decline indicates half-lives of about 5 days, which is equivalent to about 13% per day, and to a reduction to 1/1000th after 50 days (10 half-lives).

The UK is included included in the third chart for comparison. The UK Government could have made the same choices as South Korea, Australia, New Zealand and others - but its actions were too little and too slow.

The UK rate is now the fourth worst in the world, and it is declining only slowly.

The chart was generated by the online chart-drawing facility at Up-to-date charts can be obtained from there.

The data comes from the Johns Hopkins Hospital website [1].

Note on logarithmic scales

The charts are shown with logarithmic y axis scales. These compress large values and stretch out small values so it is easier to see the detail in the small numbers.

They are widely used in situation like this where there is information in both small and large numbers.


[1]Data sources

First published: 21 Apr 2020
Last updated: 2 Jul 2020