There have been more than 160 definite or probable UK cases of vCJD
Cells in the immune system could hold the key to why younger people are more susceptible to the human form of mad cow disease, scientists have said.
Patients diagnosed with variant CJD are just 28 years old on average. It has been unclear why older people have not been affected to the same extent.
Now older cells, by working less efficiently than they used to due to age, are thought to hamper the disease.
Edinburgh University scientists said it could help with vaccine development.
The researches behind the study believe the findings could also improve the diagnosis of vCJD.
Analysing mice, researchers at the university's Roslin Institute looked at how the immune system interacts with corrupted proteins, known as prions, which are linked to vCJD.
Prions accumulate in lymphoid tissues, part of the body's immune system which include the spleen, lymph nodes and tonsils, before spreading to the central nervous system, where they kill off brain cells and cause neurological disease.
The researchers found that the prions essentially "hijack" specific cells in the immune system, known as follicular dendritic cells.
The prions accumulate and replicate on the cells, until they reach a sufficient level to spread to the nerves and the brain.
But the study, funded by the Biotechnology and Biological Sciences Research Council, found that those cells were impaired in older mice.
As a result, they were unable to trap and replicate the corrupted proteins and the mice did not develop clinical disease.
Researchers said their study could explain why vCJD does not affect older humans to the same extent and why it occurs almost exclusively in young people.
Dr Neil Mabbott, of The Roslin Institute, said: "It has always been unclear why younger people were more susceptible to variant CJD and the assumption that they were more likely to eat cheap meat products is far too simplistic.
"Understanding what happens to these cells, which are important for the body's immune responses, could help us develop better ways of diagnosing variant CJD or even find ways of preventing prions from spreading to the brain. It could also help to create a vaccine."
The findings are published in the Journal of Immunology.