Updated

A pharmaceutical company has discovered stores of smallpox vaccine in its freezers, potentially bolstering the nation's inventory and ensuring an adequate supply in the event of a bioterrorist attack.

The vaccine was produced by Aventis Pasteur of Lyon, France, at its American headquarters in Swiftwater, Pa., and was discovered after the Sept. 11 attacks, according to a spokeswoman for the company in France.

Neither she, nor the company's U.S. spokesman, Len Lavenda, would provide details.

"In the interest of national security we agreed to the government's request not to discuss this matter publicly," Lavenda said.

But a spokesman for Health and Human Services Secretary Tommy Thompson said the government is discussing with Aventis whether its 70 million to 90 million doses still are effective and, if so, negotiating to buy them.

"Those discussions are ongoing and nearing conclusion," said HHS spokesman Kevin Keane.

The deal could be final as early as Friday, when Thompson has scheduled a news conference.

The vaccine has been stored in freezers since it was made decades ago, said The Washington Post, which first reported the doses Thursday. It was unclear why its existence had gone undiscovered for so long, exactly when it was discovered or by whom.

With the extra time provided by the discovery, companies will be able to fine-tune some of the new vaccine candidates under development, instead of rushing effective but perhaps less-than-perfect vaccines into production as an emergency stopgap measure.

U.S. anti-terrorism officials, guessing that terrorists could one day gain access to samples of the smallpox virus, have said the country should be prepared for a biological attack.

The vaccine must be given within a few days after exposure to smallpox, posing a logistical nightmare if outbreaks were to occur in several locations simultaneously. Smallpox has historically killed about a third of those it infects.