Thread by @ashishkjha

Lots of confusion about what Provincetown outbreak & CDC guidance mean

Mainly: how to think about spread among the vaccinated

And as importantly, what we know and what we don't

So a short thread

First, the P-town outbreak unusual

Many thousands of people (some unvaccinated) showed up to celebrate July 4

Leading to packed bars, clubs, and lots of mixing of vaccinated and unvaccinated folks in tight quarters

Ideal conditions for COVID spread

And COVID did spread

2/n

And there were a lot of infections, including among vaccinated folks

We've seen this before -- Singapore airport, Yankees clubhouse

Key issue is: did vaccines fail to

1. Prevent infection?
2. Prevent spread?
3. Prevent severe illness?

1. Did vaccines prevent infections?

Based on CDC's estimate, Pfizer/Moderna prevent about 75-85% of symptomatic infections from Delta

So if no one had been vaccinated, initial case loads would have been about 5 times higher

4/n

2. Did vaccines prevent spread among the infected?

Don't know

Study examined Ct values of symptomatic vaccinated and unvaccinated

Ct values were comparable

Driving news headlines

But single set of Ct values only loosely correlated with transmissibility

So we don't know

Did vaccines prevent severe illness?

Only 4 fully vaccinated folks ended up in hospital

None died

Those are very low rates

Consistent with theme that vaccines prevent severe illness

So yeah, they seem like they did

So what do we not know?

Because Ct values are rough surrogate of transmissibility

We don't know if actual spread among vaccinated people compare to unvaccinated

And big one: we don't know if vaccinated asymptomatic folks spread

This is key for mask guidance

5/6

Bottom line?

P-town outbreak would've been a nightmare if no one was vaccinated

Initial case #s would have been 5X

And past experience says such outbreaks fuel larger regional outbreaks

Instead, this one is fizzling out

I suspect because vaccines are working

End