Early in the spread of a new disease, its growth rate is exponential. But obviously, no disease can maintain that rate forever, it will soon run out of new people to infect. It has to level off at some point.

**At what point (at what percent of the population infected?), does exponential spread become unrealistic? **

Secondarily, how should you model the spread after that point?

(My *very* naive idea is to just model the up to 50% as exponential, and then model the next 50% as the inverse of the first half. (i.e. If weeks 1, 2, 3, and 4 had 6.25%, 12.5%, 25%, 50% infection rates, then project that weeks 5, 6 and 7, will have 75%, 87.5%, and 93.75% infection rates.) How good an approximation would that be?)

tags: coronavirsus, COVID-19

I tried this with the China data and it seems to fit well, thanks.