Officials weighing whether to dispense smallpox vaccine to the nation were presented with the possibility Saturday that the virus might be a more effective terrorist weapon than they thought.
U.S. researcher Alan Zelicoff, drawing on long-secret Soviet documents, reported on an isolated 1971 outbreak that he said appeared to have been caused by smallpox that was tested as a weapon and carried miles through the air.
If that was in fact the cause of the outbreak that killed three people, it suggests that a disease known to spread mainly in close quarters also has the potential to be used as a weapon of mass infection from farther away, perhaps from one end of a city to the other.
While Zelicoff's analysis created something of a sensation at a conference of scientists and health officials, not all were buying the theory and some were openly skeptical.
"I see nothing whatsoever that's new," said D.A. Henderson, who advises the government on bioterrorism and led the campaign that eradicated smallpox worldwide more than 20 years ago. He called the report alarmist.
Public health officials are stockpiling more than 300 million smallpox doses, enough to protect everyone in the country in the event that terrorists somehow get hold of the virus and use it to attack.
Authorities expect to have enough on hand by the end of the year.
Meantime, they are deciding whether to offer the vaccine to the public in the absence of any smallpox cases. Saturday's conference was part of a series on that subject.
The vaccine has serious side effects for many people and would be expected to kill several hundred if it were given to all Americans.
Dr. Anthony Fauci, chief of infectious diseases at the National Institutes of Health, told the meeting it is one of the least safe vaccines around, although clearly a lifesaver if smallpox makes a comeback.
The live virus is known to exist now only in heavily guarded labs of the U.S. and Russian governments, but there are fears other countries have secretly stored it and it may fall into terrorist hands.
As much death as it caused when it raged across continents, smallpox has shortcomings as a weapon, starting with the difficulty of turning it into an aerosol dispersant that can survive the elements and infect people over much distance.
It spread mainly in hospitals and homes before its eradication.
Zelicoff, from Sandia National Laboratories, analyzed Soviet documents for the Monterey Institute of International Studies in California and interviewed survivors of the 1971 outbreak that struck a port on the Aral Sea in what was then the Kazakh Republic.
Two children and a young woman died, among 10 who were infected. The seven who got sick contracted the disease despite having been vaccinated; the three who died were not vaccinated.
A Soviet report from that time indicated that the first person infected was a woman on a research vessel that sailed within 10 miles of an island where a smallpox weapons test was being done.
The woman, who is a biologist today, told Zelicoff she never left the ship during the period in question, making it unlikely she contracted the disease ashore.
Once back home, she infected her brother, who also survived, while her brother's teacher contracted the disease and died.
Officials controlled the outbreak by hurriedly vaccinating more than 50,000 people.
The disease normally kills one in three people who get it, but Zelicoff said the three who died had an extremely rare form that is almost always fatal.
For three in 10 to come down with that form, he said, suggests that the virus released in the Soviet test might have been engineered to be more deadly as well as to travel farther.
U.S. officials have been concentrating on building up stocks of the tried and true vaccines rather than on developing new medicines to counter potentially more lethal forms of smallpox.
Zelicoff said that may not be sufficient if terrorists have access to powerful strains in the form of a weapon.
"We cannot be satisfied with making 300 million doses of the old vaccine, as good as they were," he said in an interview.
Henderson challenged Zelicoff point by point. For one, he said the Kazakh outbreak could have come naturally from nearby Afghanistan, which is known to have had smallpox cases in 1971.
"This doesn't suggest we have anything that is unusual," he said.