The end of exponential growth: The decline in the spread of coronavirus | The Times of Israel

A similar pattern – rapid increase in infections to a peak in the sixth week, and decline from the eighth week – is common everywhere, regardless of response policies

The following is the text of a study by Prof Isaac Ben-Israel, first published on April 16, 2020. (Ben-Israel discussed his research on Israeli TV on April 13, saying that simple statistics show the spread of the coronavirus declines to almost zero after 70 days — no matter where it strikes, and no matter what measures governments impose to try to thwart it.)

Our analysis shows that this is a constant pattern across countries. Surprisingly, this pattern is common to countries that have taken a severe lockdown, including the paralysis of the economy, as well as to countries that implemented a far more lenient policy and have continued in ordinary life.

It turns out that a similar pattern – rapid increase in infections that reaches a peak in the sixth week and declines from the eighth week – is common to all countries in which the disease was discovered, regardless of their response policies: some imposed a severe and immediate lockdown that included not only “social distancing” and banning crowding, but also shutout of economy (like Israel); some “ignored” the infection and continued almost a normal life (such as Taiwan, Korea or Sweden), and some initially adopted a lenient policy but soon reversed to a complete lockdown (such as Italy or the State of New York). Nonetheless, the data
shows similar time constants amongst all these countries in regard to the initial rapid growth and the decline of the disease.

For example, our calculations show that the pattern of the daily new infections as a percentage of accumulated number of infections (weekly averaged), is common to every country around the globe. Typically, in the first phase of the spread, this percentage amounted around 30%, decreased to a level of less than 10% after 6 weeks, and ultimately reached a level of less than 5% a week later.


Note: The exponential GF of 1.15 is used to show means of comparison of infection growth rate. Notice Italy peaks at about 30 days; Sweden peaks about 37 days, yet the two countries took drastically different approaches in response to the outbreak.

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