https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1114482/
The wiki also indicates that a sheep vaccine distributed in 1935 caused an epidemic, as it contained contaminated neural tissue:
https://en.wikipedia.org/wiki/Scrapie
It also seems to me that the recent mRNA vaccines could be repurposed to target a section of a prion, so the immune system could clean them from the blood. An interesting question would test mRNA vaccine effectiveness in the cerebrospinal fluid, where microglia would be required to perform this function, as macrophages (and friends) are not present there.