An Irish based drug company has developed a vaccine which could be useful in the treatment of Alzheimer's Disease.

The vaccine was developed by Elan Corporation, plc, and was used to treat mice genetically engineered to develop Alzheimer's.

When given to young mice the treatment prevented the build-up in the brain of the protein deposits always seen in Alzheimer's patients. In older mice which already had the "plaque" deposits the vaccine cleared them away, the researchers reported this morning in the science journal, Nature.

It was not clear whether the vaccine would work in humans, stated the company's executive vice president for corporate development, Mr Seamus Mulligan. Nor was it known whether the removal of the plaques would bring an improvement in a patient's condition. There was disagreement amongst scientists whether the plaque is the cause of the brain damage and dementia brought by the disease or only a side effect.

"It is our contention that it is the plaque build-up that causes the degeneration," he added. If proven to be so, and if the vaccine could be changed for use in humans, then the company may actually be able to arrest the progress of the disease, either halting it or actually reversing it.

The company, he said, had one of the largest Alzheimer's research groups working in any pharmaceutical company, with investment in its research centres in the US, Ireland and Israel reaching more than $200 million. The research work was done by its California-based laboratory, acquired when Elan purchased Athena Neurosciences, Inc in 1996.

Elan would submit an "Innovative New Drug" application to the US Food and Drug Administration before the end of the year, Mr Mulligan said. This would licence the company to conduct limited trials of the vaccine in human patients. It would take some years before any successful treatment reached the market, he added.

Elan was the only company known to have used the vaccine approach against this disease, he said. The treatment was based on using a small part of the plaque's chemical make-up to create a vaccine. Once given, the vaccine prompts the mouse's own immune system to attack and break down the plaque deposits, which form along the nerves in the brain.