[nostromo]

That wouldn't account for places like Spain and Italy that are both sunny and more pedestrian friendly that were hit harder than the US though.

The theory that makes the most sense to me is that East Asia has had exposure to past viruses that were similar in nature but less lethal.

> Tatsuhiko Kodama of the University of Tokyo said preliminary studies show that Japanese people’s immune systems tend to react to the novel coronavirus as though they had previous exposure, and notes that there are centuries of history of coronaviruses emerging from East Asia.[1]

1. https://www.washingtonpost.com/world/researchers-ponder-why-...