[saalweachter]

There was a recent study of dialysis patients: https://www.thelancet.com/journals/lancet/article/PIIS0140-6...

TLDR: "During the first wave of the COVID-19 pandemic, fewer than 10% of the US adult population formed antibodies against SARS-CoV-2, and fewer than 10% of those with antibodies were diagnosed."

[Animats]

That's for the month of July 2020, which is useful, but not enough. We need trend data for this.

[nradov]

The trends won't really tell you much as we get further into the pandemic. Just because someone lacks a detectible level of antibodies doesn't necessarily mean they are susceptible.