DAVIS, Calif. - (KRT) - Within a week, the Bush administration will likely release its plan to protect the country from a bioterrorist attack using smallpox, one of the world's oldest, most contagious and most feared diseases.

Health care workers, police, firefighters and other first responders will undoubtedly be vaccinated under the plan, but the administration is still deciding who else should receive the sometimes dangerous vaccine, according to D.A. Henderson, the National Institutes of Health's bioterrorism adviser and leader of the original smallpox irradication campaign in the 1970s.

The plan likely will not call for large-scale, mandatory vaccinations, like those ended 30 years ago when the virus was irradicated, Henderson said Thursday. He was speaking before doctors and public health officials at a University of California, Davis-sponsored conference on bioterrorism and new emerging diseases.

Thirty years since the U.S. stopped regularly vaccinating the public, 80 percent of U.S. citizens are susceptible to smallpox, either because their immunity has worn down or they were born after 1972. That means the country would be particularly vulnerable to an attack.

"The effective dose is just a few … particles. And that is what worries us," Henderson said, as he showed a slide of the disease's surprising spread through a German hospital in the 1970s. "It is a low probability, but if it were released, it would be such a catastrophe that we can't afford not to deal with it."

One vaccination plan could allow those concerned about bioterrorism to request the vaccination, but they would have to understand the risks. If 100 million people were vaccinated, 100 to 400 people would likely die. Another 2,500 would have serious, potentially fatal complications. There is also a small possibility that smallpox could be passed from the vaccinated people to those around them.

"Those of us who have treated cases, we are concerned how widely we vaccinate," he said.

The timescale for both plans is still being worked out. Around 500,000 hospital personnel likely to treat a smallpox victims would be vaccinated first, Henderson said. They would be followed by vaccinations for 10 million other first responders.

Smallpox is named for the thousands of puss-filled blisters that show up in the middle of the disease. About 30 percent of those who get the disease die, another 70 to 80 percent are permanently scarred by the blisters, and others are left blind. Even now, there is no real treatment for smallpox except prevention.

Scientists like Henderson say not everyone needs to be vaccinated to be protected. Smallpox victims are not contagious until they start showing serious flulike symptoms, about 12 days after exposure. That means if scientists know people are exposed they can isolate them before they infect others. People can also be vaccinated up to three days after they are exposed without getting the disease.

But that only works if doctors have access to the vaccine. That was a problem when the United States first became serious concerned about the issue after Sept. 11, but now they have about 200 million doses, which would be plenty to vaccine those who have been exposed.

"We have gone from having no vaccine to being well prepared," Henderson said.

Henderson did say that the hype over genetically engineered smallpox seems to be overblown. Of the strains he has seen, including those from the former Soviet Union, none seem much different from the worse strains he saw in India. But scientists can still think of some pretty scary scenarios, including flu pandemics, hantaviruses, Ebola and other diseases discussed at the two-day conference.

"I, in a way, resent the need for myself and others to spend time on a thing like small pox when there are other things that need to be done," he said.

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