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Comment by tghw | Hacker News Reader

CDC Data from mid June had NYC at only 20% prevalence. Considering their low new daily cases since then, it's hard to believe they are anywhere near 68%.

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So, I think the proposed math is something like: 1/3rd of infected don't show antibodies so that 20% means 30% were infected. Another study showed pre-existing T cell reactivity (maybe immunity?) in 40% of people, so if you combine those you're at 70%.

I find it hard to believe, with the R0 numbers we were seeing initially, that 40% had a significant level of immunity. If the numbers were that high, then R0 among those without memory T-cell immunity would have been significantly higher, which suggests that the level of exposure/immunity necessary for herd immunity to set in would be significantly higher as well.

What you're saying makes sense. Looking at some tables of it, it seems like if we imagine it in a naive population having a 50% higher reproduction number, it seems like it only bumps the herd immunity number by about 10% because it is such a high proportion already, if I'm understanding the charts right. It isn't clear if the numbers come together, but it does make me wonder if it could be close.

NYC data from August has some boroughs as high as 51% https://www1.nyc.gov/site/doh/covid/covid-19-data-testing.pa.... The 68% comes from this article https://www.nytimes.com/2020/07/09/nyregion/nyc-coronavirus-.... The data appears to be from doctor's offices- not sure we can access that actual data (but I didn't try that hard to get it).

68% tested positive at a clinic in one neighborhood. Getting tested, without proper controls, is highly subject to self-selection bias. People were sick, couldn't get a test at the time, want to know if it was COVID, go in for an antibody test later. The people who were healthy, unless selected for a prevalence study, would much less likely to be tested in the first place.

Even in your first link, the highest percent positive is the Bronx reporting 33%. Not sure where you're getting 51% from, but it very much seems like you're trying to cherry pick data to support your argument.

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