The University of Iowa is one of three institutions nationwide participating in a follow-up study aimed at increasing current stocks of the smallpox vaccine.

The study is sponsored by the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health.

The UI portion of the investigation is being led by UI Health Care investigators Patricia Winokur, M.D., and Jack Stapleton, M.D. Winokur and Stapleton also are researchers and staff physicians at the Veterans Affairs Medical Center in Iowa City.

Nearly 150 participants, ages 18 to 32, have been invited to take part in the trial. Most people in the United States in this age group have never been vaccinated against smallpox because common use of the vaccine ended in 1971, Winokur said.

Smallpox is thought to be one of the most concerning diseases that could be used in the event of bio-terrorism. Current estimates are that 120 million Americans are susceptible to smallpox, which has a 30 percent mortality rate.