The researchers evaluated how immune system cells responded when participants were exposed to vaccinia, a virus related to the smallpox virus used in vaccines to trigger immunity to smallpox.

What were the results of vaccinia exposure?

Exposure to vaccinia produced a robust response in people who had been vaccinated in recent years. The response was still considerable in people who had been vaccinated 6 to 35 years before. People who had been vaccinated more than 35 years ago still had a considerable immune response.

When was the smallpox vaccine used?

The smallpox vaccine was required for school entry in the U.S. prior to 1972. About 60 percent of the US population is vaccinated. The eradication of smallpox was officially declared in 1980, and according to the World Health Organization, national vaccination programs stopped in all countries by the early 1980s.

What are the symptoms of smallpox?

The initial signs of smallpox infection include headache, vomiting and fever. Then pus-filled lesions form on the head and face, and may also appear on other parts of the body.

What treatments exist for smallpox?

There is no treatment for the disease, which is fatal 20 percent to 40 percent of the time in unvaccinated people. However, if an individual has been exposed to the virus and is vaccinated within the next 4 days, the vaccine can reduce symptoms or prevent the disease.

Does smallpox still exist?

Officially, smallpox exists in only two laboratories -- one in the US and the other in Russia. However, there are some concerns that other organizations may have samples of the deadly virus.

The New England Journal of Medicine August 29, 2002;347:689-690