Emergence of variant type of Creutzfeldt-Jakob disease (vCJD) in humans due to infection from bovine spongiform encephalopathy contaminated beef and recent reports of human-to-human transmission of vCJD via blood transfusion have raised great concern about an epidemic of vCJD. The disease is currently difficult to diagnose during pre-clinical stages and requires a very long incubation period for neurological symptoms to be evident. This therefore suggests that the disease is already latently spreading and that opportunity for infection is thus growing among human populations. Interestingly, passive immunization with antibodies against prion protein (PrP), a major component of the prion infectious agents, was shown to protect mice from infection, indicating the possibility of prion vaccines. However, PrP is a host protein therefore immune tolerance to PrP has hampered development of them. Here, the so far reported attempts to overcome the tolerance to elicit protective immunity to prions are briefly reviewed.