China. I think it has helped all areas that had an overwhelming ramp in infections (NYC, Northern Italy, Wuhan). I don't think he's suggesting China has reached herd immunity (although it wouldn't surprise me if Wuhan had a substantial portion of the population infected), but if that's what you're saying "there's no evidence of", I retract my Hoothat insult.

I have just seen a lot of statements like "we don't even know if people who are infected have immunity" which sounds scary, but flies in the face of everything we know about viruses, so I find it a bit frustrating. Yes, this is a new virus, so anything is possible I suppose, but I think there are so many far more realistic things to worry about than this being a virus so unlike any other that antibodies help defeat the virus initially, but then are helpless against it just weeks or months later.