The smallpoxvaccine prevents smallpox. For most people, it is safe and effective. Most people experience normal, typically mild reactions to the vaccine, which indicate that it is beginning to work. Some people may experience reactions that require medical attention.
This can happen if you eat nerve tissue (the brain and spinal cord) of cattle that were infected with mad cow disease. Over time, vCJD destroys the brain and spinal cord.
There is no evidence that people can get mad cow disease or vCJD from eating muscle meat-which is used for ground beef, roasts, and steaks-or from consuming milk or milk products.
People with vCJD cannot spread it to others through casual contact.
People who have spent a lot of time (at least 3 months) in places where mad cow disease has been found are not allowed to give blood in the United States or Canada.2, 1 This is to help prevent vCJD from spreading.
What causes mad cow disease and variant Creutzfeldt-Jakob disease (vCJD)?
Experts are not sure what causes mad cow disease or vCJD.
The leading theory is that the disease is caused by infectious proteins called prions (say "PREE-ons"). In affected cows, these proteins are found in the brain, spinal cord, and small intestine. There is no proof that prions are found in muscle meat (such as steak) or in milk.
When a cow is slaughtered, parts of it are used for human food and other parts are used in animal feed. If an infected cow is slaughtered and its nerve tissue is used in cattle feed, other cows can become infected.
People can get vCJD if they eat the brain or spinal cord tissue of infected cattle.
How common are mad cow disease and vCJD?
The first case of vCJD was reported in 1996. Since then, there have been a few cases of vCJD reported in the world. Most of the cases have been in countries that are part of the United Kingdom (England, Scotland, Wales, and Northern Ireland).