Yellow Fever
Yellow fever is a mosquito-borne viral disease that is endemic in 44 countries in tropical regions of Africa and South America. The disease is transmitted to susceptible persons when they are bitten by infected mosquitoes. Large epidemics can occur when the virus is introduced into areas with high human population density. Domestic mosquitoes carry the virus from person to person.
Infection causes a wide spectrum of disease, from mild symptoms to severe illness with bleeding and jaundice and death. The "yellow" in the name is explained by the jaundice that affects some patients.
There are 200,000 estimated cases of yellow fever (with 30,000 deaths) per year. However, due to underreporting, only a small percentage of these cases are identified. Small numbers of imported cases also occur in countries free of yellow fever. Although yellow fever has never been reported from Asia, this region is at risk because the appropriate primates and mosquitoes are present.
There is no specific treatment for yellow fever. Vaccination is the single most important measure for preventing yellow fever. Vaccination is highly recommended for travellers to high-risk areas. A vaccination certificate is required for entry to many countries, particularly for travellers arriving in Asia from Africa or South America. Fatal cases in unvaccinated tourists have been reported. The vaccine is a live attenuated vaccine. YF 17D vaccine is the only commercially available vaccine against YF. Yellow fever vaccine is safe and highly effective. The protective effect (immunity) occurs within one week in 95% of people vaccinated. A single dose of vaccine provides protection for 10 years and probably for life.
More than 400 million doses of YF vaccine have been administered worldwide with an excellent record of safety, although mild systemic reactions such as headache and weakness occur during the first few days after vaccination in 10.30% of vaccinees. Severe adverse reactions are extremely rare, but when they do occur infants and the elderly seem more susceptible than the YF-vaccinated population at large.
WHO recommends that countries at-risk for YF incorporate the 17D vaccine into their national immunization programme. As of 2006, 78% of the at-risk countries in Africa where YF vaccination is recommended, have incorporated YF into EPI. However, routine YF vaccination coverage remains low with only 52% of countries achieving 80% coverage by the end of 2006. In the at-risk countries of South America, YF vaccination has been used for decades, coverage rates of more than 80% have been achieved in countries and in enzootic areas of 10 countries in the region.
WHO Position Papers
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WHO position paper on Yellow fever (October 2003) in English and Frencg
pdf, 339kb - WHO position papers in Arabic, Chinese, Russian and Spanish
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References
pdf, 89kb
Related links
Last updated: 15 October 2008