I read an article a few days ago that indicates that there are currently 7 or so nations that haven't had a confirmed case of the Kung in quite some time...
Most of them have one thing in common.... they're isolated as hell and surrounded by thousands of miles of Pacific ocean, with few visitors in and out.
A couple are also extremely low population Asian nations (IIRC a couple are former Soviet Republics) in very mountainous regions, which naturally promoted limited contact/exchange between population groups.
Then there's North Korea. Anyone believe that North Korea has had zero cases of the Kung? Anyone? Anyone? Well, apparently the WHO, does, but apparently WHO can't explain the Nork's dramatic and sudden rise in lead poisoning deaths of the last year...
Of course, the Norks were the first nation in the world to completely close their borders once things started hitting the fan, which our lovely left found to be heroic, justified, and prescient... Trump doing the same thing, however? It just shows what a racist xenophobe he is!