The high R0 low mortality rate model, or what you might call the optimistic model, was in fact very plausible and very much promoted by some experts back in January and early February.
So, in a discussion on Friday, the speaker had a very interesting point that we may gain significant leverage on the disease not based directly on its R0, but on the second moment of R0, the
variance of R0.
So... consider two diseases:
Generic influenza - while there's some differences in strains, broadly, it has an R0 of about 1.3.
Ebola - has an R0 of about 2.
Based on that alone, we'd expect ebola to be a highly prevalent disease. However, it is influenza that just about everyone in the world gets. Why? Because R0 is an average, and we have to then consider the spread of values that make up that average.
The R0 of influenza is about 1.3, and there's not a whole lot of variance in it - if three people get influenza, you can put good money on how they will together infect four more people. Between its intrinsic properties and how we deal with it... influenza is relentless and almost like clockwork.
Ebola... is not. There's a high variance in its R0. A lot of folks who get ebola never pass it to anyone else. And a small number of victims of the disease are responsible for "superspreader" events - passing it on to 20 more, instead of just 2. So, on broad average R0 is small.
And, that's how you deal with ebola - you crack down on the superspreader events, and what is left is an R0 too small to sustain itself, and the outbreak dies out.
So, when we look at the preliminary R0 for covid-19, we are looking at that average, and we have to wonder whether it is that, if one person has it they
reliably pass it to 2.5 more people, or if most folks with it don't pass it on at all, and that a few are responsible for large spreading events.