Yellow fever as an endemic/epidemic disease and priorities for vaccination.

Yellow fever is a potentially fatal viral hemorrhagic fever. Although an effective vaccine (yellow fever 17D) has been available since the late 1930s, utilization is incomplete in many areas, particularly in Africa, with the result that yellow fever epidemics still occur. Official reports of yellow fever between 1965 and 2004 in South America and Africa total over 33,000 cases. In West Africa, a major resurgence of epidemic yellow fever occurred in the late 1980s to the mid 1990s, and epidemics continue to occur nearly every year in some location. Attack rates in these outbreaks have averaged about 5%. Yellow fever infections occur unnoticed during periods between epidemics, but the endemic disease burden in Africa is difficult to quantify due to insensitive surveillance. Based on estimates of the infection rate, the inapparent/apparent infection ratio, and the population adjusted for vaccine and naturally-acquired immunity, the annual incidence of endemic yellow fever in Africa is estimated at between 24 and 240 thousand, with the principal burden of disease in childhood. Significant progress has been made over the last 5 years in the introduction of yellow fever vaccine into routine childhood immunization programs in Africa. Vaccine coverage in South America is at a respectable level in the endemic region. However, vaccine policy in non-endemic coastal regions of South America must weigh the risk of vaccine-related adverse events against the theoretical benefit of preventing urban yellow fever.