@ Thegreatunwashed:

Quote:

I wonder if the Diamond Princess is really quite the perfect natural experiment as it seems, at least in one specific respect. Being a cruise, I imagine it is possible that a large portion of the passengers got heavy doses of natural vitamin D that they normally wouldn't get when not on vacation. That may have boosted their innate immunities and saved many of them from infection.

I doubt it. A typical 1 to 2 week cruise isn't enough sun time to really boost your Vit D by a significant margin.