A vaccine to protect against Alzheimer's disease, which proved encouraging on animals, is now being tested on humans.

A vaccine to protect against Alzheimer's disease, which proved encouraging on animals, is now being tested on humans.

The potential vaccine is being tested on a group of 80 patients, all aged over 60, who have developed the first symptoms of the degenerative brain disease. It is hoped that the first phase of the clinical trials will be completed this summer. If the vaccine proves successful, it could transform the way the illness is treated.

Dr Mike Hall, an Alzheimer's specialist, said: "It's too soon to say if it will be successful but it's potentially very exciting because it may be that we'll be able to prevent Alzheimer's."

Alzheimer's is the most common form of dementia, affecting nearly 500,000 people in the UK and 12 million worldwide. But the total is forecast to rise to 22 million by 2025 as the over-65 population doubles.

Three drugs have been approved for prescription on the NHS, all of which aim to stabilise early symptoms such as memory loss, confusion and personality change. But there are concerns that patients are being denied the drugs because some health authorities are reluctant to pay the high costs.

A successful vaccine would hold out the prospect of screening people for Alzheimer's and immunising those at most risk, or possibly vaccinating everyone as they reach middle age.

Experiments on mice have already shown that the vaccine can prevent the build-up of protein deposits in the brain, called plaques, which are believed to cause Alzheimer's.

In a study published last year, researchers demonstrated how the vaccine prevented memory loss and arrested the disruption of nerve cells in mice which were specially bred to mimic the onset of the disease.

Now the vaccine, being developed by Elan Pharmaceuticals, is undergoing parallel trials in the UK and America to see if it produces any adverse reactions and to investigate whether it triggers the production of protective antibodies. If the vaccine passes these tests, it will have to undergo full-scale clinical trials which means at least another five years before it could be licensed for public use.

Dr Richard Harvey, head of research at the Alzheimer's Society, said: "We're hoping to hear this summer whether the vaccine has worked, whether it's generating antibodies, then a decision will be taken about moving up to the next phase."

News of the trials came as the Association of the British Pharmaceutical Industry released a report charting medical research into 13 potential new drugs to treat the condition, the possibility of developing a urine test to diagnose the disease and progress with the vaccine.