[Thread]

Certain Hasidic communities have stopped social distancing two months ago, and there seem to be few mask-wearers.

Yet, there has been no detectable rise in infections.

It's a shame that this data isn't being properly collected and analyzed, because it could potentially provide important insight as to the upper bounds of infection rates, and other key questions.

Absent real data, here's what we do have: https://twitter.com/MarcusBlimi/status/1264587394398945280

Could it be that these communities have achieved herd immunity (1-1/R0) with approx. 60%?
I believe that this is unlikely for many reasons, but mostly because it's unlikely that R0 in these communities was ever 2-3.

R for Measles in the Hasidic community is estimated to be at least 2X R0 in other populations, as Dr Daniel Berman explains here: https://www.nydailynews.com/opinion/ny-oped-vaccination-is-not-an-ultra-orthodox-jewish-hangup-20190515-jppvzaabqfcm3cku2erlp7piry-story.html

If R0 for Covid-19 in Hasidic communities is 5, we would need 80% immune to achieve herd immunity. With far higher contact rates in Hasidic communities, it's unlikely that 60% is enough.

On the other hand, if R0=5 it's hard believe 40% was not exposed to the virus. To demonstrate:
3^10=59,049.
5^10=9,765,625
At 10 transmissions, Hasidic communities should be infected at a rate of 165/1 relative to median population.

Perhaps the answer is that there were more infections, but seroprevalence isn't the best measure of covid-19, because there are other types of immune responses, as shown in this preprint: https://twitter.com/VeodLekra/status/1275595420954234881

It's also possible that there's heterogeneity in susceptibility, in part maybe because of those same immunity mechanisms or other factors. https://twitter.com/VeodLekra/status/1270696237851914240

In other words, maybe there's an upper bound to covi susceptibility.

Interestingly, we now have the first controlled observational study, the Antarctica cruise ship, and 59% was the upper bound of covid infections, based on PCR testing

The Antarctica cruise may not be typical because they took precautions immediately after the index case was discovered. Still, it's interesting that seroprevalence in Williamsburg and PCR testing on the cruise had roughly the same numbers