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DURHAM, N.C. -- Duke University Medical Center researchers are conducting a study to determine whether diluted amounts of smallpox vaccine are effective in boosting immunity from smallpox in previously vaccinated adults. The results of the trial will help guide national policy for distributing smallpox vaccine in the event of a bioterrorism attack using smallpox.

The Duke study is part of a multicenter trial sponsored by the National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health (NIH) that will examine whether the current supply of smallpox vaccine could be diluted for distribution to a larger number of people without hampering the vaccine's ability to protect against the virus.

"Basically, we're trying to determine how far the current supply of smallpox vaccine could be stretched, if needed" said Emmanuel Walter, M.D., associate director of the Primary Care Research Consortium of the Duke Clinical Research Institute, and the leader of the Duke study. "If a diluted dose still provides immunity against smallpox in the population who were vaccinated more than 20 years ago, then we would be able to make the existing supply of vaccine available to a much larger group of people."

Smallpox virus is considered one of the most lethal biological weapons that could be used in a terrorist attack against the United States. Smallpox is a highly contagious viral disease that causes such symptoms as fever, malaise and severe rash, and is fatal in approximately 30 percent of cases. There is no known effective treatment for smallpox.

Although the disease was declared eradicated worldwide in 1980, small quantities of the smallpox virus still exist in research laboratories around the world, and security experts speculate that terrorists could acquire samples of the virus for use in an attack against the United States.

Routine smallpox vaccination ended in the United States in 1971. People who received the vaccine prior to 1971 have little immunity remaining and would not be protected in the event of a smallpox outbreak. Although the Centers for Disease Control and Prevention stores a supply of smallpox vaccine, none has been manufactured in 20 years, and the existing supply would not be adequate to treat the entire U.S. population.

For the study, the Duke team will recruit approximately 90 volunteers between the ages of 32 and 70 years who were previously vaccinated against smallpox. The volunteers will receive either a full dose of smallpox vaccine, a dose of vaccine diluted to 20 percent strength, or a dose diluted to 10 percent strength. The volunteers will be followed for several months as physicians measure their levels of immunity against smallpox. The Duke team will also monitor and report any side effects volunteers develop from the vaccine.

"We're excited about this project," said Walter. "It's a great opportunity for Duke and residents of the Durham area to contribute to the development of national public health policy."

Also participating in the NIAID study are the University of Rochester, the University of California Los Angeles, Northern California Kaiser-Permanente, the University of Maryland, St. Louis University and Stanford University.

Duke will begin screening potential study volunteers this month. Individuals interested in participating in the study should call (919) 668-8627.