Bob Alvey, a spokesman for the state Department of Health, said about 935 Arkansas residents have been vaccinated but no incidents of side effects have been reported. He said the program will remain shut down until the Centers for Disease Control, which is investigating the deaths of three people who died of heart attacks after receiving the vaccine, can provide more information about possible risks.

"We've always known and acknowledged that there are serious but extremely rare risks associated with the vaccine," he said.

It remains unclear whether the three heart attack deaths were related to the vaccine, but at least 10 states have suspended their vaccination programs. Known possible risks include severe rashes, blindness and infections.

Health officials at the Atlanta-based CDC are investigating the deaths.

Dr. William Mason, the ADM Bioterrorism Preparedness Team Medical Leader, said all volunteers are screened to minimize the possibility of side effects. He said the deaths prompted the CDC to add having a history of heart disease or three or more cardiac risk factors to the list of factors to be considered.

Alvey said Arkansas' program began in March and is in its first phase, providing the vaccine to members of public and hospital response teams who would be on the front line should a case be found in the state.

The second phase would inoculate doctors and nurses, police and fire workers, paramedics and others public disaster workers. The general public would be provided with the vaccine in the final phase.

The program will not restart until CDC investigators have completed their review and can provide more information on risk factors, Alvey said. He said there is no timetable for resuming vaccinations. Officials hope to inoculate up to 10,000 Arkansas residents.

"We feel like we're vaccinating enough people to respond in the unlikely event we have a case of smallpox," he said.