The last naturally acquired case of smallpox in the world occurred in October 1977 in Somalia; global eradication was certified two years later by the WHO and sanctioned by the World Health Assembly (WHA) in May 1980. Except for a laboratory associated smallpox death at the University of Birmingham, England, in 1978, no cases have been identified since. All known variola virus stocks are held under security at the CDC, Atlanta, Georgia, or the State Research Centre of Virology and Biotechnology, Koltsovo, Novosibirsk Region, Russian Federation. In response to concerns that variola stocks may be needed for counterterrorism research in the event that clandestine stocks held by other countries fall into terrorist hands, the WHA in May 1999 authorized that the virus be held at laboratories in USA and Russia until no later than 2002. WHO reaffirmed that destruction of all the remaining virus stocks is still the organization's ultimate goal and will appoint a group of experts to consider what research needs to be carried out before the virus can be destroyed. WHO will also set up an inspection schedule for the two laboratories where the official stocks are kept to make sure that they are secure and that research can be carried out safely.

Because of the potential use of clandestine supplies of variola virus for biowarfare or bioterrorism, it is important that health care workers become familiar with the clinical and epidemiologic features of smallpox and how it was distinguished from chickenpox. Even though strains of virus used for biowarfare might have been engineered so that clinical differences may result, past experience with naturally occurring variola remains the best guide to recognition and management of an epidemic pox virus disease.