The virus exists in any number of animal reservoirs, so it is already endemic.
“The virus exists in any number of animal reservoirs, so it is already endemic.”
Which, like flu, makes it impossible to eradicate and gives it more ability to mutate.
Polio doesn’t infect animals which is one reason that that vaccine was so successful. And the polio virus itself isn’t as unstable. Only 3 wild variants.
Smallpox is another virus with no known animal or insect reservoirs. And therefore a highly effective vaccine, or what is known around here as “a REAL vaccine” as opposed to all of those pretender vaccines that have to try to beat down a seemingly endless stream of variants coming at them.