Thread by @petermbenglish

It's not really R0 now.

R0 is the reproduction number (the average number of people infected by each case when 0% of the population is immune to the infection. The 0 (which should be subscript) is the %ge of the popn which is immune.
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But R0 also implies the normal operation of society. With Covid-19, when people were behaving normally, the R0 was somewhere around 4, but probably with considerable variance: some cases were infectious but with no/minimal symptoms, so they infected more people…
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… Whereas others got too ill to go out, so infected fewer people.

The R value is a function of the virus, and of behaviour. It will be higher (when there's fomite transmission) in hand-shaking cultures, for example.
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The lockdown is all about changing behaviours. By reducing proximity, you reduce airborne spread (face-coverings likely reduce it further); and by reducing contact, and increasing handwashing, you reduce fomite spread.
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The effect is to reduce the number of people, on average, infected by each case. This is a new R value. It is no longer R0, but rather, the _effective_ R value: Re (again, the e should be subscript).
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Before I finish, I've noticed R described in various places - including Sunday's Boriscast - as a rate. A rate is one number divided by another. R is a number, not divided by anything. It is the R NUMBER, and NOT a rate.
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It's true that when you know the average interval between cases, you can use the R value and that interval to calculate something like a rate. But that is not R.
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@threadreaderapp This thread has been smartened up slightly and turned into a blog, complete with a spreadsheet:
peterenglish.blogspot.com/2020/05/common…

See blog version: peterenglish.blogspot.com/2020/05/common…