Atlanta ? Concluding that the medical risks of the smallpox vaccine outweigh the threat of a potential outbreak, an advisory panel for the Centers for Disease Control and Prevention Thursday decided not to recommend reinstating a national immunization program that would have made the vaccine available to the public.

As the federal government moves to safeguard the country against a potential biological attack using the smallpox virus, the panel recommended vaccinating up to 20,000 medical workers, such as ambulance drivers, emergency room workers, epidemiologists, law enforcement personnel and others designated as first responders should there be an outbreak.

The recommendations developed by the CDC’s Advisory Committee on Immunization Practices, a 15-member group of medical experts, have been forwarded to the U.S. Department of Health and Human Services, which will use them as guidelines for developing a national policy on smallpox.

“We all have a degree of discomfort over not knowing exactly how much of a threat exists,” said committee chairman Dr. John Modlin. “We believe this nicely balances the risks we know for the vaccine with the risk of smallpox even occurring, which we have been told is very low.

“We think this is the best policy under the circumstances,” Modlin said. “If there is ever a real threat, the policy could change.”

Smallpox, a highly communicable and deadly disease, has not been detected in the United States since 1949 and was declared eradicated from the world in 1980. Smallpox causes death in about 30 percent of its victims, according to doctors.

The vaccina vaccine, a live virus that is the only inoculation available against smallpox, has not been administered routinely in the U.S. since 1972. The vaccine can cause severe rashes and brain swelling, and is estimated to cause at least one death for every 1 million people vaccinated. The risk is greater among people with skin disorders and immune diseases such as HIV.