Truth be told.

@The_Whore_of_Blahbylon that's not quite fair. We have also discovered a lot about hygiene, preventing disease, food, hormones, vitamins, healthy and unhealthy practices.
It is known that vaccines that prevent the deadliest diseases actually work. But, I don't know, for instance, if there are (known) side-effects that are taken for granted because they were preferable to likely death. And we know part of the medical world operates within a conflict of interest.