The vaccine targets a bad form of tau protein. A company already did clinical trials with a medecine targeting bad tau protein. The company is called TauRx Pharmaceuticals. They did a clinical phase II with 350 people. The results were awesome. Disease progression was reduced by 80 % !!! This means that if you would have Alzheimer for 10 years, you would be in the situation of a person having Alzheimer for only 2 years. They planned to do a clinical phase III with it and the medecine would be available in 2012. However, they started a clinical phase III a bit later with a better similar medecin. They say this trial will finish in 2013.
Also, more and more evidence is showing that the tau protein is the one causing all the damage. They genetically reengineered mice to produce a lot of human tua in a certain region of the brain. Scientist found that these tau proteins when misfolded, started to attack neurons and spread from neuron to neuron and killing all neurons in its path.
I am happy for those people suffering with Alzheimer ... this seems like a real breakthrough. You will soon all have a very important disease modifying medicine and/or vaccine.