Repeatedly invoking the threat of terrorism, the Senate on Wednesday unanimously approved a $5.6-billion, 10-year initiative to encourage private industry to develop vaccines and drugs that would protect Americans from biological, chemical or nuclear attacks.

If terrorists have access to anthrax, smallpox, botulism toxin, plague or Ebola virus, said Sen. Judd Gregg (R-N.H.), "there is no question they will use it. And they will use it in a place where people gather to go about their daily lives."

The Senate vote came more than two years after anthrax-filled letters caused five fatalities, changed the way mail was inspected and delivered, and highlighted the nation's vulnerability to bioterrorist attacks.

President Bush, who on Wednesday praised passage of the bill as "another important step in winning the war on terror," proposed Project Bioshield in his 2003 State of the Union address. The House passed a bill, 421-2, last summer, but the legislation stalled in the Senate over the technical concerns of a handful of lawmakers.

Edward Jenner, the English physician who first developed the smallpox vaccine in 1796, believed that vaccination caused a fundamental change in personal constitution and would lead to lifelong immunity to smallpox. Unfortunately, this proved to be incorrect. It is now clear that immunity wanes over time. Exactly how long the vaccine confers protection, however, is difficult to assess.

As early as Monday (2002-12-02), President Bush is expected to order smallpox vaccinations for 500,000 U.S. military personnel and 510,000 civilian medical workers as a precaution against a biological attack by Iraqi agents or other terrorists, administration officials say.

Smallpox, or variola virus, is considered by many doctors to be the pathogen most dangerous to the human species. The virus was eradicated as a natural disease 25 years ago, and is now stored legally at only two sites: in a freezer at the Atlanta headquarters of the Centers for Disease Control and Prevention and at a Russian government laboratory in Siberia. Research on the virus is being conducted at both sites, but is tightly restricted by the World Health Organization. In 1972, the United States stopped giving routine vaccinations for the virus.

Now fears about smallpox have returned, with the possibility that this biological agent will be used as a weapon in terrorism or war. A number of countries, including Iraq, Iran and North Korea, are suspected by United States intelligence agencies of keeping clandestine stocks of smallpox for use as a weapon.