The biggest fear is that these cases may presage an epidemic. At this time, the mortality risk of vCJD is not quantifiable. The original mathematical model used by a team at Oxford University predicted 500,000 human deaths in the United Kingdom over the next several decades. More recently, they predicted anywhere from 63 deaths to 136,000 deaths.5 Precise mathematical modeling is hampered because of many unknown variables. Their wildly varied assumptions, ranging from .0001 to 10 cases of vCJD per infected cow, reflect the basic lack of knowledge about the disease infectivity.
Incubation is another wild card.
Iatrogenic CJD incubates anywhere from 15 months to 30 years, while kuru incubates up to 30 years. Researchers suspect that vCJD may have a varying incubation period, too. The longer the incubation period of vCJD, the grimmer the ultimate prognosis becomes. In addition to uncertainty over mortality data, concerns have been raised about the safety of the blood supply. Although it has not been proven that vCJD is transmissible by human blood, animal experiments have resulted in successful transmission by transfusion in sheep.