In the aftermath of the events of September and October, 2001, there is heightened concern that the variola virus might be used as an agent of bioterrorism. The deliberate release of smallpox is now regarded as a possibility, and the United States is taking precautions to deal with this threat.
The Centers for Disease Control and Prevention (CDC) calls the variola virus a "Category A" agent. Category A agents are believed to present the greatest potential threat for harming public health and have a moderate to high potential for large-scale dissemination. Other Category A agents are:
Smallpox was described in Asia during the first century, in Europe and Africa around 700 A.D., and in Central, South, and North America during the 16th and 17th centuries. Some health experts believe that smallpox, over the centuries, has been responsible for more deaths than all other infectious diseases combined.
Thanks to the success of a worldwide vaccination program, smallpox has been eradicated. The last naturally occurring case in the world was in Somalia in 1977. In 1980, the World Health Organization officially said that smallpox was wiped out worldwide, and no cases of naturally occurring smallpox have happened since.
After variola virus was eliminated from the world, routine vaccination against smallpox among the general public was stopped because it was no longer necessary for prevention.