A vaccine against Alzheimer's has come a step closer to reality after scientists succeeded in preventing the build-up of toxic brain proteins linked to the disease.

Experiments on mice showed that the DNA vaccine, injected into skin, could potentially delay the onset of Alzheimer's with no serious side-effects.

Scientists said the findings, published in the journal Alzheimer's Research And Therapy, could pave the way for clinical trials with human patients.

Two kinds of toxic protein or protein building blocks are thought to play a key role in Alzheimer's, beta-amyloid and tau.

Beta-amyloid accumulates in sticky clumps in the brain and is a characteristic hallmark of the disease seen in patient post-mortem examinations.

Tau is a protein which produces destructive "tangles" within nerve cells. Some research suggests that the two are linked, with beta-amyloid promoting the formation of tau tangles.

The new vaccine contains DNA coding for a segment of the beta-amyloid protein building block, or peptide.

In the study the vaccine triggered an immune response that not only led to a 40% reduction in beta-amyloid build-up, but also reduced tau formation by 50%.

The research was conducted on mice which were genetically engineered to develop a rodent equivalent of Alzheimer's disease.

A major obstacle to developing effective Alzheimer's vaccines has been finding safe ways to introduce them to the body.

One previous experimental vaccine developed in the early 2000s caused brain swelling in some patients when tested on humans.

The new vaccine is injected into skin instead of muscle, which leads to a different kind of immune response.

If repeated in humans, the effects seen in mice would have "major therapeutic value", said the researchers.

"If the onset of the disease could be delayed by even five years, that would be enormous for the patients and their families", Co-author of the study Dr Doris Lambracht-Washington said.

"The number of dementia cases could drop by half", she said.