The total numbers of cases of yellow fever in 1992 and 1993 were relatively low, but noteworthy in that the first outbreak recorded in Kenya since 1943 was documented. A total of 295 cases were reported to WWO for 1992, with 102 deaths (case-fatality rate (CFR), 35%). These included 176 cases and 21 deaths (CFR, 12%) from Africa, and 119 cases and 81 deaths (CFR, 68%) from South America. In 1993, a total of 218 cases and 38 deaths (CFR, 17%) were reported from Africa, and 175 cases with 79 deaths (CFR, 45%) were documented from South America, for a grand total of 393 cases and 117 deaths (CFR, 30%). A summary of the number of yellow fever cases and deaths reported to WHO by Member States for the period 1989-93 is shown in Table 1.
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In a dramatic decrease in the number of cases reported compared with previous years, only Kenya and Nigeria reported yellow fever in 1992, while Ghana experienced a limited outbreak in 1993 that continued into 1994.
Ghana. In 1993, an outbreak of yellow fever occurred in the Upper West Region, with 39 cases and 15 deaths (CFR, 38%).(m) The outbreak began in October 1993 and cases were still being reported in December. Transmission appeared to be limited to the Jiripa District. Yellow fever was confirmed serologically. Of 37 cases where age and sex were reported, 15 (40%) were under 15 years of age, and 9 (24%) were females. An immunization campaign was begun in December 1993 and continued into 1994; it appears to have controlled the outbreak.
Kenya. The first yellow fever outbreak reported from Kenya since 1943 began in September 1992 and continued through March 1993. The outbreak was limited to the Baringo and Elgeyo Marakwet Districts in the Kerio Valley, north-west of Nairobi. A total of 54 cases and 28 deaths (CFR, 52%) were recorded. Eighteen of the cases (33%) were among people aged [less than or equal to] 19 years and 19 cases (35%) were females. Epidemiological investigations indicated that the outbreak was consistent with jungle yellow fever. The virus was isolated from clinical specimens of ill and fatal cases, and from captured mosquitos. Molecular characterization of the isolated viruses indicated that they were similar in genetic composition to those previously isolated from humans and mosquitos during past outbreaks of yellow fever in East Africa, and genetically distinct from isolates from specimens collected in West Africa or South America. The outbreak was halted following a mass immunization campaign, during which nearly 1 million doses of yellow fever vaccine were administered to residents of the areas at risk.
Nigeria. Only 149 cases and 8 deaths (CFR, 5%) were reported from Nigeria in 1992, unlike the situation in recent years when several thousand cases were documented. In 1993, 152 cases were reported, with eight deaths (CFR, 5%). No information was provided on the specific dates of onset, locations, age or sex of the reported cases for either year.
EPI: yellow fever vaccine in Africa. Since 1989, WHO/EPI has recommended that yellow fever vaccine be included in the childhood immunization programmes of the 33 countries in Africa at risk for the disease. Today, 17 of the 33 countries have a national policy to this effect. Up to August 1994, yellow fever immunization coverage data had been reported to WHO by 15 of the 17 countries. Burkina Faso, the Gambia, and Mauritania have achieved coverage above 50% for children by their first birthday. However, for all 33 African countries at risk for yellow fever, vaccine coverage levels only reached 7% in 1993, compared with 11% in 1992.
The African countries at risk are among the most impoverished countries in the world. Although yellow fever vaccine is available to developing countries at less than US$ 0.25 per dose, this price is still a barrier to many countries at risk. Donors are encouraged to provide assistance to help the African countries at risk prevent the deadly disease through routine immunization. …