Researchers are starting to think that Alzheimer's disease could be caused by microbial infections that cause plaque to form in the brain. This opens the possibility for a vaccination against Alzheimer's.

Support for the immune defence idea comes from work by Jacobus Jansen of Maastricht University in the Netherlands. Using MRI brain scans, his team has found that people in the early stages of Alzheimer's disease have more permeable blood-brain barriers, suggesting that they may have developed the disease because their brains were more vulnerable to attack. "The microbe hypothesis seems plausible," says Jansen.

If infectious agents are kicking off the formation of plaques, then vaccines could head them off. "You could vaccinate against those pathogens, and potentially prevent this problem arising later in life," says Moir.

If many microbes are involved, immunising against them all will be hard, says Jansen. "But if the frequency of certain pathogens is quite high, there might be a possibility."