Abstract
There occurred during the planning and publication of this review: the twentieth anniversary of the start of the intensified WHO Smallpox Eradication Campaign and the tenth anniversary of the last endemic case of smallpox; debate about the fate of smallpox virus and possibly its irrevocable destruction; claims that mass smallpox vaccination campaigns may have helped the spread of AIDS in Africa; publication of the definitive account of Smallpox and its Eradication (Fenner et al. 1988), and the closure of the WHO Smallpox Eradication Unit (SEU). It is therefore perhaps an appropriate moment to assess the current status of human poxvirus infections and their epidemiology; this review concentrates on those viruses antigenically related to smallpox (i.e. orthopoxviruses).