The prototype vaccine has proved effective at combating the disorder in mice suffering from the human form of the degenerative brain disease, which affects more than 400,000 people in Britain and is estimated to cost the country pounds 5.5bn a year. The number of affected individuals is likely to rise by 50 per cent over the next 40 years because of the ageing population.
The vaccine works by stimulating the body's immune system to produce antibodies against the protein deposits, known as plaques, that build up in the brain of Alzheimer's patients. The experiments, published in the journal Nature, showed that the vaccine was highly effective at preventing protein plaques appearing in the brains of susceptible mice inoculated at an early age. A second experiment on older mice who had already developed signs of Alzheimer's disease demonstrated that the vaccine effectively prevented the disease from worsening.
Dr Dale Schenk, who led the research team from Elan Pharmaceuticals, a San Francisco drug company, said the results were far more clear-cut than he ever expected. "It was a dramatic result. I would have been satisfied with a 20 or 30 per cent reduction in plaques but we actually got something like 90 per cent," he said.
Other scientists who have seen the work but have no connection with the company said the vaccine has the potential to become the first effective treatment for what is currently an incurable condition. Although the appearance of protein deposits is a distinguishing feature of Alzheimer's disease, scientists are unsure whether they cause dementia or are a by- product of nerve degeneration. "If we can clear plaques... the next question is whether we can block the onset of dementia," said Peter St George- Hyslop, professor of medicine at the University of Toronto.
Elan Pharmaceuticals plans to apply for permission to begin human clinical trials before the end of the year but it will take many more years before a vaccine can be used routinely on patients, Dr Schenk said.