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In 1967 and 1968, Sierra Leone had the highest incidence of smallpox in the world. In 1969, the disease was eliminated from the country. This paper describes the epidemiology of smallpox before and during the Smallpox Eradication Program. Smallpox epidemics have occurred in Sierra Leone at intervals of about 10 years since 1946. In epidemic years, peak transmission occurred during the late dry season and early rainy season. Smallpox was predominantly a disease of rural villages with less than a thousand inhabitants, in which the attack rate in 1968–69 was 55.2 per 100,000, as compared to 9.5 in towns of more than a thousand persons. Attack rates were highest in diamond-mining and cattle-raising areas. Persons of all age groups and both sexes were affected, with a slight predominance in children less than 15 years old. Case fatality ratios averaged 11.1%, with the highest proportion of deaths occurring in infants. Social patterns favoring intimate contact, such as funerals of smallpox victims, were important sources of widespread outbreaks. Characteristics of 15 patients who introduced the disease into previously uninfected communities are compared.
Present address: Department of Pediatrics, University of Chicago, Chicago, Illinois 60637.
Present address: State and Community Services Division, Center for Disease Control, Atlanta, Georgia 30333.
Deputy Chief Medical Officer, Ministry of Health, Freetown, Sierra Leone.
Present address: Director, State and Community Services Division, Center for Disease Control, Atlanta, Georgia 30333.