
WHO study on Covid-19: We estimated that the median of estimated R0 is 5.7 - paganel
https://wwwnc.cdc.gov/eid/article/26/7/20-0282_article
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Endlessly
If R0 is truly 5.7 - roughly 82.46% of the population must become immune
before “herd immunity” kicks in.

((R0 − 1)/R0) is known as the “herd immunity threshold” — that is, with an R0
value of 5.7 the computation would be ((5.7 - 1)/5.7) or 82.46%

Learn more here, — “Herd Immunity”: A Rough Guide:
[https://academic.oup.com/cid/article/52/7/911/299077#3862683](https://academic.oup.com/cid/article/52/7/911/299077#3862683)

As a comparison, here are the R0 values of other well-known infectious
diseases:
[https://en.m.wikipedia.org/wiki/Basic_reproduction_number](https://en.m.wikipedia.org/wiki/Basic_reproduction_number)

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berberous
I read this recently:

I've noticed a fair number of people assuming the herd immunity threshold, 1 -
1/R0, is the total proportion of the population infected. It isn't; it's the
proportion of the population immune (i.e. has had the disease; in this model
that's assumed to confer immunity) at which the epidemic stops growing. The
total proportion of the population infected is called the epidemic final size
(I'll call it 'F'), and is given by

F = 1 - e-R0*F

This is higher. Lots higher. For R0 = 2, it's 80%. For R0 = 3.4 (the WHO
estimate), it's 96%.

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Endlessly
Appreciate the information, though citing notable sources might help others
understand and add credibility too.

For example, “Herd immunity & epidemic final size” covers the topic:

[http://alizon.ouvaton.org/Report2_Immunization.html](http://alizon.ouvaton.org/Report2_Immunization.html)

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glofish
Obviously that can't quite be universally right, look at Brazil, look at
Malaysia, India. Look at Easter Europe. It is pretty clear it can't be 5.7 all
across the board.

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joe_the_user
Ro is the spread without mitigating factors, so Ro is more or less assumed
constant.

That said, there's no reason to think the particular places you're naming are
either doing effective testing or mitigating factors. People tossing around
the statistics of a given country without looking deeply at the testing
process have been confusing the situation for a while here.

Moreover, a lot of these quotes wind-up wrong as they're stated. "Look at
Eastern Europe". I can see fast exponential in Romania, maybe other parts of
the area are still in "don't ask, don't tell" but doesn't prove anything.

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glofish
we will see, but it is just hard to fathom that with all these social
distancing measures in place you still have 400K in the US and seemingly very
few in Brazil and all these other places where for large swaths of the
population social distancing is not an option.

It might be that the R0 is far more variable than assumed.

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dragontamer
> social distancing measures in place

R0 is the measurement of what will happen WITHOUT social distancing.

In effect, researchers calculate R0 to determine if social distancing /
lockdowns / etc. etc. would be worthwhile.

\------

The virus's real reproductive rate is called "R" (which is obviously lower
now, due to social distancing / masks / etc. etc.). R0 is the "if we did
nothing" variable.

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Cpoll
What's the correct way to say 'R0 with social distancing?'

That is to say, R0 in a hypothetical place that was always practicing social
distancing?

Because as I understand it, R0 is used to calculate herd immunity, but a lot
of people are curious about what the herd immunity numbers would look like if
we continued to take measures such as 6ft/2m distancing and wearing masks
(efficacy debated, I know) and face shields.

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et2o
This does not seem to be a WHO study, as far as I can tell?

~~~
tastroder
Yeah, not sure where op got the "WHO" part of the title from, the site says:
"Author affiliations: Los Alamos National Laboratory, Los Alamos, New Mexico,
USA"

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sphix0r
Based on Chinese data. I very much doubt the accuracy of Chinese data.

