Thread by @ashishkjha

Watching Delta variant take off across world

What will it take to control it?

Vaccines & public health measures of course

Here in US, we're abandoning PH measures (masks, distancing)

So vaccines

How much?

My estimate: 60% of Americans fully vaccinated

We're at 46%

Thread

So why is 60% a reasonable estimate?

Well, lets begin with R0 of Delta

Best credible estimates suggest its around 5

If you had no public health measures, need 80% population immunity to stop spread of the virus

Immunity comes from two sources:

Vaccines
Prior infections

2/n

If 46% have been fully vaccinated,

means 54% not yet fully vaccinated (math!)

But (and this is surprisingly contentious), folks with prior infection obviously have some degree of immunity

Let’s assume they have as much immunity as vaccinated people (I'm not sure they do)

3/n

And while vaccinated (and previously infected) folks can have breakthroughs

Let's assume they don’t transmit to others (largely true)

(I'll go back and check my assumptions at end)

So how many unvaccinated folks have been previously infected?

Best guess for US? 36.5%

Seems real precise. Did I just make that up? No

CDC estimates that by mid-April, 114 Million Americans had been infected and recovered

In last 2 months, we’ve probably added about 6M more

So that’s 120M infected/recovered or 36.5% of the US population

5/10

I'm going to assume that previously infected folks got vaccinated at same rate as others

You can make case on both sides

So math:

330M Americans - 153M fully vax = 176M not fully vax * 36.5% natural immunity

Means 64 million unvaccinated people with natural immunity

6/10

Add 64M (unvaxed, immunity ) to 153M fully vaxed

217 million people immune

That’s 66% of the population!

But not anywhere near 80%

So we need to vaccinate another 14%

Another 46M people

If we vaccinate another 46M folks, we'll be at 60% of the population fully vaxxed

7/10

So that should be our target – 60% of Americans fully vaccinated

OK fine, that's math

But what about reality?

Israel at 59%. Why wasn't that enough?

Partly b/c I believe they have less natural immunity (likely had fewer infections than US)

So they need higher threshold

8/10

So how do we think about this?

First, we have 26M Americans who've gotten one shot but not yet 2nd

Half of them are in 3-4 week waiting period and will

Which will bump us to 166M fully vaxxed

Another 13M missed 2nd shot. If they get it,

we'll be 29M short

Not bad

9/11

But lets check some assumption

What if unvaccinated more likely to be previously infected?

Than we need less than 60%

What if the R0 closer to 7 as some have argued? Then we need about 66% vaccinated

What if we keep some public health measures? We'll need less

So forth

But 60% of population fully vaccinated is reasonable target

Is that crazy undoable?

No

VT is at 65%.

MA, ME, and CT are above 60%. RI is at 58% -- almost there

So yeah, its doable

I know we have work to do in other states

11/12

So here we are

Delta

Most contagious variant we've seen so far

It is wreaking havoc around the world

And will cause problems here

Not horrible spikes but real problems

We arent done yet

Lets get 60% of Americans fully vaccinated

And get this Delta thing under control

Fin