Where in the world did you hear that feeders/pet mice and rats are vaccinated? There are no such vaccines that exist.

You eat cattle that are vaccinated, it works the same way. We live, the snakes would be fine if the feeders "were" vaccinated. But since they aren't, it's a moot point.

And fancy mice are the same as "feeder" mice. Most of my breeder mice and feeders are "fancies", brindles, black&white, silver brindles, long haired, rex, etc. They seemingly taste just as good to the snakes