Now that Dr. Fauci is saying we may need up to 90% immunization for herd immunity, I'll say what I've been thinking in a wonkier way. 1/ https://www.nytimes.com/2020/12/24/health/coronavirus-herd-immunity.html?smtyp=cur&smid=tw-nytimes

We don't know R0, the inherent rate of spread of SARS-CoV-2, and we won't know for some time.

Pulling it out of the data is a statistical operation and needs a lot of data. Additionally, the data are lumpy - that's what people are talking about in "superspreaders." 2/

I get annoyed that people confuse R0 with what I'll call R but goes by many names.

R is the measured rate of spread for a particular situation. For example, New Mexico has recently gone from R = about 1.3 to R = about 0.86. Which is good. 3/

The reason R has decreased for New Mexico has very little if anything to do with the virus itself or R0. It's because people are acting more responsibly and staying home, wearing masks, practicing hygiene. 4/

But we don't know how much of that decrease is due to staying home, how much to wearing masks, and so on. Modelers are estimating those effects, but they're very hard to get at. 5/

That's the kind of analysis that is needed to get to R0. And we don't know what percent immunization is needed for herd immunity until we know R0. At the same time, watching how transmission decreases with levels of immunization will help us estimate R0. 6/

We're getting more and more data, which is why Dr. Fauci feels confident about the numbers he's using.

It's clear that SARS-CoV-2 won't be easy to control. But we control measles, and it needs 95% herd immunity. 7/

A big part of the reason that SARS-CoV-2 is so out of control is that NOBODY was immune to it. But we're getting to a better place. 8/8

I've written this thread up as a blog post. https://nucleardiner.wordpress.com/2020/12/24/dr-faucis-warning/