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The last case of endemic smallpox occurred in Somalia in 1977, and eradication of the disease was declared in 1980. With no natural reservoir, variola virus, which causes smallpox, has existed only in laboratories; indeed, the last case of smallpox was due to infection acquired in a laboratory in the United Kingdom in 1978. During the global program of smallpox eradication, the World Health Organization (WHO) made concerted efforts to decrease the number of laboratories retaining variola virus. On the basis of contacts with all countries and a total of 823 microbiology institutions, 76 such laboratories had been identified by . . .
Breman et al. (2002) studied this question.