In tests, psoriasis disappeared in a quarter of cases and half saw an improvement. Benefits lasted for 18 months.

Psoriasis is a disfiguring genetic condition, which affects at least one in 50 people in the UK, making it as common as rheumatoid arthritis and diabetes.

It is thought to be caused by a malfunctioning of the immune system, which causes accelerated growth of skin cells.

These cells pile up on the surface of the skin when the body cannot shed them fast enough, leading to unsightly patches of raised red skin covered by a flaky white build-up.

The condition tends to affect people first in their twenties, though people can carry the gene and not suffer from the condition.

Treatment can currently either be with a drugs or with a cream.

Psoriasis is rarely fatal, but the psychological damage people can suffer because of the disfigurement can have a devastating effect on their lives.

It can flare up because of stress or severe throat infections.

Vaccine hope

The vaccine, developed in New Zealand appears to "turn off" part of the immune system.

The researchers say that a single shot can offer long-lasting protection.

The vaccine was tested on 24 patients with psoriasis. Larger trials are now being carried out.

Researchers carried out the trial after tests of an anti-leprosy virus in India had failed to cure leprosy, but had cleared up one patient's psoriasis

That vaccine contained microscopic organisms called Myobacterium vaccae which had been killed using heat treatment.

The New Zealand team used the same preparation in their vaccine.

Dr James Watson, the Auckland researcher who led the trial, said most research concentrated on trying to find the proteins which trigger the disease.

Instead his team had concentrated on changing the response of the immune system.