Thread by @ASlavitt

BREAKING: NY reduces its infection rate below 1, a major milestone in the COVID-19 battle.

But what does that mean? I asked Bill Joy, one of the smartest people around when it comes to pandemics & Sun Co-founder.

He’s allowing me to share it here. 1/

The infection rate, or r, is simply the number of people each infected person infects. It makes an enormous difference.

With r of 2.3, after just 10 cycles, 1 person infects 4100 people. At 1.3, 1 person infects only 14 people. 2/

That reduction means hundreds of fewer hospitalizations & dozens fewer deaths.

This is why we launched the #StayHome campaign & states focused on isolation measures. 3/

An r < 1 is an achievement. If sustained it means the virus’s spread actually lessens— at least as long as that is sustained or until it is re-introduced. Say by a visitor from South Dakota. 4/

From an r that at one point was > 2 and according to some measures, potentially even higher, that happens for 2 reasons— aggressive social distancing & growing herd immunity. (There is anecdotal evidence which suggests NY could have 15-20% herd immunity.) 5/

Bill points out that NY reporting a 0.9 r is certainly progress but may not be enough.

Wuhan, which operates under much more authoritarian measures, reduced r to 0.3. And that he reminded me is an enormous difference. 7/

To quote Bill:

The process of getting to open in Wuhan lasted, if memory serves, 79 days, the majority of it at 0.3.
0.9^11=0.31, i.e. it takes 11 times as long at a rate of .9 to get the same result as at 0.3.
Unimaginably long, but that’s what the data says. 8/

NY has over 200,000 positive confirmed cases and is still adding ~10,000/day, not to mention the untested cases. Far more than Wigan. And that’s far too many for a public health workforce to trace & contain. 9/

For NY to emerge as cleanly as Wuhan, Bill calculates that would take over a year unless r continues to decline— not to mention all the travelers from S. Dakota & elsewhere. 10/

The so what is more & more of the same. Effective masks, social distancing to get cases to decline & through the system while testing capacity ramps.

And as goes NY so goes CT & NJ. 11/

NY likely won’t wait until they achieve Wuhan levels of infection spread before they open. But with an asymptomatic virus, a lot of testing, infrastructure, reduced r & more time are still needed. 12/

Can’t help but be encouraged by this progress but also realistic about how not to have to go back to this point again.

Thanks Bill. If he had amendments/changes I will add them later. /end