A group of prisoners who appear to be naturally immune to hepatitis C could lead to a vaccine, Australian researchers hope.
Tattooing can transmit hepatitis C
The University of New South Wales team is studying four prisoners who became infected yet went on to clear the virus with no symptoms.
Similar immunity has been found in some Kenyan prostitutes against HIV.
The authors told the Journal of Infectious Diseases they hope to mimic this natural defence with vaccines.
It is estimated that 170m people world-wide are infected with hepatitis C, and that many more are at risk.
The virus, which can be passed through sexual contact or by the mixing of blood through things like transfusions or sharing drug equipment, can cause fatal liver problems.
Some patients - some 20% - manage to get rid of the hepatitis C virus within six months without ever suffering the symptoms of the disease.
In the remainder, the virus can remain in the body, again perhaps not causing any symptoms, for even a period of decades.
However, if the liver inflammation begins to get worse, then symptoms can appear.
Professor Andrew Lloyd and colleagues studied 160 prisoners who were free of hepatitis C infection but were at high risk of contracting the virus because of their lifestyles - injecting drug use or tattooing.
They collected blood samples from the prisoners on a monthly basis for over a year.
Four of the prisoners became infected with hepatitis C during this time, yet they all went on to clear the virus without developing any of the symptoms of the disease.
Surprisingly, none of them developed antibodies against the virus.
Instead, it appeared that another arm of the immune system based on specialised white blood cells, called T cells, were employed by the body to ward off the disease.
Professor Lloyd said: "It is possible that they had been infected in the past, perhaps on several occasions and that may be why they were able to clear the virus efficiently without developing antibodies.
"Vaccine strategies to mimic this response may provide protection against persistent hepatitis C virus infection," he said.
Scientists are already developing vaccines against hepatitis C, but some of these treat rather than stop infection.
There is currently no licensed vaccine to protect against the hepatitis C virus.
A spokeswoman from the British Liver Trust said: "It's really quite phenomenally important research.
"Although the phenomenon has been recognised before, no research has been published on it. This is the first.
"It's quite clear that there is a whole cohort of people who do not develop hepatitis C. "
She said the findings would be key to getting a vaccine.
"Getting a vaccine is the holy grail of hepatitis C at the moment and it looks like this is getting towards that," she said.