eradicated from the planet one virus that afflicts humans, and that s smallpox. that s eradication. elimination means where you haven t eradicated it from the globe, but you ve essentially eliminated it, for example, from a given country, take the united states. so what have we done? we ve done that with measles, and we ve done that with polio with. but there were three factors that went into our ability to do that. one, measles and polio is not a virus that changes. the measles that we had 20, 30 years ago is the same measles we have right now. number one. number two, either infection-induced or vaccine-induced immunity is virtually lifelong. and ors as a matter of fact, that s what we had. and then you have a very, very effective widely acceptable and widely accept ised vaccination campaign. that s why we were able to eliminate it.