Technically, you're correct, but the 1957 flu "came back" in 1968, and again in 2009 if I recall correctly. Yes, I'm sure they were never completely gone, but

Technically, you're correct, but the 1957 flu "came back" in 1968, and again in 2009 if I recall correctly. Yes, I'm sure they were never completely gone, but at some point there are enough non-resistant people and it flares up again, and we would want to have better options for that "next time". But yes, technically, you're correct, it will never quite go away.