WASHINGTON?The nation will have a lot more smallpox vaccine than previously thought in case of a bioterror attack: New research shows 15 million stockpiled doses can be stretched to make up to 10 times more and the government is negotiating to buy millions of doses discovered in a drug company’s freezers.

Both discoveries are important because, while the government has ordered 200 million new doses to be made by a British company, they won’t arrive until at least year’s end and then must pass testing to ensure they’re safe and effective.

Having more vaccine already on hand would buy more time to make sure the new production is done properly.

The nation quit routine smallpox vaccination in 1972, and the disease was declared eradicated worldwide in 1980.

The U.S. and Russian governments hold stocks of the deadly virus, and bioterrorism experts worry that samples could fall into terrorists’ hands and be used as a weapon.

So the government has been working to get enough vaccine for every American, just in case. If an attack occurred, doctors would quickly vaccinate people in the vicinity, because inoculations up to four days after exposure still offer protection. There are no plans yet to resume routine vaccination, because the vaccine can cause some severe, even fatal side effects, and until now, there wasn’t enough available anyway.

That may no longer be the case.

Some 15.4 million doses are in a government stockpile. That vaccine could be diluted, turning each dose into five to 10 additional doses, and still be protective, say two studies released Thursday by The New England Journal of Medicine. The studies of more than 700 previously unvaccinated young adults found about 97 percent responded to diluted or undiluted inoculations, although some required two doses.

One catch: A few people never responded, and blood tests suggest they had been vaccinated decades earlier but had forgotten. Thus, more study is needed to tell if diluted vaccine can boost the presumed waning immunity of millions vaccinated 30 years ago, wrote lead researcher Dr. Robert Belshe of St. Louis University.

Pennsylvania-based Aventis Pasteur has told the government it has 70 million to 90 million doses of smallpox vaccine sitting in its freezers, stocks federal health officials hadn’t thought existed.

Aventis now is checking whether that vaccine still is effective after so many years, and the government is discussing whether to buy it.

“Those discussions are ongoing and nearing conclusion,” said Kevin Keane, a spokesman for the Department of Health and Human Services. Details of a deal could be announced as early as Friday.

Now that so much more vaccine seems available, “it’s time for an open public debate?on whether it makes sense to vaccinate the public preemptively,” said Dr. Jeffrey Drazen, editor of The New England Journal of Medicine.

If all Americans were vaccinated, experts estimate 180 to 400 people could die just from the inoculation’s side effects.

In the latest studies, no one became severely ill. But one person had blister-like lesions erupt over a swath of his body. More than a third had pain bad enough to miss school, work or other activities. Fever, headache, nausea, muscle aches, lesions and swelling were fairly common.

One expert argued in the journal that routine vaccination should begin, because waiting until an attack could cost more lives. Vaccinating in advance would better protect people with weak immune systems, who are most at risk from the side effects, and avoid the mass panic sure to ensue if smallpox ever appears, wrote William Bicknell of Boston University.