(CBS) Health and Human Services Secretary Tommy Thompson is asking Congress for $1.6 billion to fight bioterrorism, including money to buy an additional 300 million doses of smallpox vaccine.

Smallpox? That's right.

"The administration," says Thompson, "is taking aggressive steps to make sure that our country is well-protected from bioterrorism."

CBS News Correspondent Sharyl Attkisson reports the probability of attacks with biological weapons - contagious ones like the plague and smallpox - is considered to be extremely remote. But the consequences are so devastating, the government is working out scenarios for swift response.

Americans haven't been vaccinated for smallpox since 1971 and protection from most of those shots has worn off.

Johnathan Tucker, a bioweapons expert, wrote a book on the risk of smallpox being used as a weapon.

"The risk as assessed is low," says Tucker, "but the consequences are so great that we need enough vaccine on the shelf to deal with this contingency if it ever occurs."

Oklahoma Governor Frank Keating took part in a simulation last June called "Dark Winter" - designed to test response to a fake smallpox outbreak.

In the drill, complete with mock news reports, there was a vaccine shortage and so much panic, the government resorted to martial law. The findings have now taken on new meaning.

"The dark winter exercise was a wakeup call, says keating. "we know very little if anything about smallpox, or bubonic plague or for that matter anthrax until last week."

There is a shortage of smallpox vaccine, and even before the September attacks, US officials were pushing to produce more - and faster. They may be able to stretch what there is by watering it down. It's highly effective, but only if given before symptoms show up. So early detection of any outbreak is crucial.

Asked whether he believes an outbreak would be quickly recognized by physicians seeing the symptoms for the first time, Tucker says he's "not confident...that would be the case."

But doctors are more likely now to recognize such symptoms than they would have been just a short time ago.

Experts say that's the good, if such a thing can be said, that's come out of this: an increased awareness, which will help the U.S. to be better prepared if it ever does have to respond to a bioterrorist attack of that nature.