There also appears to be a difference in the strains. The NYC strain seems to mostly come from the European branch, while the CA infection comes directly from China (and likely much earlier in 2020). There appears to be some difference in virulence between the strains.

https://www.medrxiv.org/content/10.1101/2020.04.08.20056929v...

and

https://nextstrain.org/ncov/global

I’ve never looked into that (I know of the hypothesis, though) but IFR in South Korea also seems to be around 1% (or higher), not 0.1%

Can you elaborate?

Percentage of people with antibodies is similar (if you take those studies at face value).

Percentage of people dead is not.