I mean look at the Bubonic Plague. Today it will shows up occasionally in animals or humans, Herd immunity back in the 13th-17th century eventually stifled the plague. There were no vaccines, only herd immunity and the threat is basically gone. You say 30% of Europe's population was killed by the Black Death? They would have died anyway, right? Influenza Pandemic (Kansas Flu) of 1918-1919, no vaccine, that stain of Influenza is no longer a threat. Herd Immunity once again. 50 MILLION worldwide died? They would have died anyway. Columbus visits Hispaniola in 1492. There were about a million inhabitants when he stopped by and left Smallpox. Of course there was no vaccine back then, but we had herd immunity for the 500 out of the 1,000,000 that were around a couple of generations later. So yeah, history proves that herd immunity works.