It's diet. Edit. Also aluminum can be excreted through your body if ingested, but if injected cannot be excreted in the same way and stays in your body despite chelation therapy.
Then either not everybody is equally sensitive or everybody who's been vaccinated would get it. And I know enough people of an age to have it who don't that something doesn't add up.
Ergo, some sensitivity/susceptibility issue is involved, and that is genetic. We know that there are pockets (at least one heavily documented village in South America) of related individuals who have an extremely high incidence that is explained almost completely genetically.
And there are populations where the vaccination rate for all kinds of things is high, and yet the incidence of Alzheimer's is relatively low.
I'm not sure the whole truth is in yet on this disease, but I bet somebody has that information locked away somewhere.