The Washington Post is carrying this article summarizing a surprising effect of a failed attempt at an Alzheimer vaccine:

An experimental vaccine for Alzheimer's disease, which was quickly pulled from testing last year after it caused serious side effects, has halted and even reversed the brain disease in some who got the shots, according to the first follow-up study of those patients.

The gist of the article is that, while this particular attempt is too dangerous to proceed with, it does seem to indicate scientists are on the right track.