Strengthening national preparedness for smallpox: an update.

Concern that smallpox virus may be used as a biological weapon of mass destruction has prompted calls for production of additional vaccine and new research into variola virus diagnostics and clinical interventions. Only 15.4 million doses of smallpox vaccine, produced approximately 20 years ago, exist in the United States (1). While virtually all lots remain potent, additional vaccine would clearly be needed in a national emergency involving smallpox virus. Global eradication of natural smallpox disease was declared in 1980; with eradication, most research activities involving the virus ended. Although the complete genomic sequence of selected isolates of variola virus is known (2), the diagnosis and treatment of smallpox infection have not changed in the past two decades. Recognizing the need for advancement in these areas before variola virus stocks are destroyed, the World Health Organization (WHO) passed a resolution (WHA 52.10) in 1999 extending the date of destruction of all remaining variola virus stocks until the end of 2002. The midpoint of this period is an appropriate time to review progress made in vaccine production and variola virus research and to outline the next steps.