This should be something that can/will be resolved by testing. I find it unusual that no medical authority is going on record as saying there's any long term immunity granted by infection, and that the WHO is being extremely clear in the lack of evidence to support such a conclusion.
Greedo, no. haha. They're not on record yet because the tests are under way. Had they found an early failure that shakes the foundations of medical science, they'd have shared it. Especially in this news cycle which overwhelmingly favors negative information.
It's like saying "I find it very strange no scientists came out on record this week with a study showing water remains wet -- does it?! How can we tell if we don't check again."
Lack of proof of an affirmative is not proof of a negative, and especially not when plenty of other evidence points in the direction of the affirmative (again, not conclusively).
