1(a) - Why does this distinction matter?
1(b) - I don't know.
2 - The current medical consensus is that not only has it not been eradicated -- it likely never will be.
Definitely mass hysteria.
To a partial extent it was. But it defintely wasn't simply a matter of mass hysteria.
Are you wiling to recognize that reality can sometimes have conflicting qualities -- e.g. there can be simultaneously "too much of a reaction" against a perceived threat; but also "some kind of serious response was needed; no one could possibly have known at the time what the optimal response would have been; sometimes it's better to err on the side of caution"?
Especially in regard to things like once-per-century pandemics, which are obviously still poorly understood?