A Belgian company is developing the therapeutic vaccine, which treats rather than prevents a disease.

It is one of five such vaccines currently being developed.

The hepatitis C virus is carried in the blood. It is very hard to treat and can cause fatal liver problems.

We have to be very cautious

Nigel Hughes, British Liver Society

It can be transmitted via blood transfusions or if drug users share needles.

The liver can fail completely or become cancerous, and hepatitis C is the most common reasons for liver transplants.

Existing treatments only cure around half of those infected.

They can also cause serious side effects, such as severe depression.

The World Health Organisation estimates that around 170 million people have hepatitis C.

In the UK 200,000 are estimated to be affected, most of whom are unaware they have the disease.

Improvements

The therapeutic vaccine, which is being developed by Belgian Innogenetics, is based on a protein found on the virus's coat.

The company tested the vaccine on 24 patients who, on average, had had hepatitis C for 19 years.

The patients were given five injections of the vaccine every three weeks and another six injections after a six month interval.

Liver biopsies were taken before and after the treatment.

Researchers found the vaccine appeared to prevent liver scarring and inflammation from getting worse in most patients.

We have to be very cautious

Nigel Hughes British Liver Trust

In the nine who had the strongest response to the vaccine, the condition of their liver was seen to improve.

Its makers stress further work, including research comparing patients who had been given the vaccine with those who have not, is needed to confirm the findings.

The vaccine seems to work without altering viral load, the amount of virus in the blood which scientists look at to assess the severity of viral diseases.

The researchers say this may mean that while the viral load may reveal the effectiveness of drugs that stop a virus replicating, it might not be a true indicator of how serious a disease is.

Variation

But experts said, although new treatments were welcome, there was so far insufficient evidence that the vaccine was effective.

Nigel Hughes, chief executive of the British Liver Trust, told BBC News Online therapeutic vaccines had been developed for other diseases, but had "come to nothing".

He added: "This is a very small study. Biopsies are a good way of diagnosing liver disease.

"But in terms of monitoring disease, there can be a variation because of the observer, and this is one sample from the largest solid organ in the body.

"So we have to be very cautious."