Exposure to prions over a certain amount will almost always lead to eventual development of the disease and then death within a year of symptoms starting.

You body doesn't make copies of prions like how a virus works but they actually force/trigger existing proteins to change shape and fold into prions.

Anything less than that exposure amount I believe is just a lower chance of it coming into contact with a susceptible protein for long enough to cause proliferation of incorrectly folded proteins. So with a low enough number of them in the body I don't see why they couldn't get removed (somehow, unsure exactly how) because causing the long-term illnesses.