Introduction
Yellow fever (YF) is a viral hemorrhagic fever. It is transmitted to human by Aedes aegypti, mosquitos infected with the YF virus. The case-fatality rates can exceed 50% among severe cases. YF can be prevented through immunization with the YF vaccine, which is safe, inexpensive and reliable. A single dose of the vaccine provides protection against the disease for at least 10 years and possibly throughout life. A high risk exists of an explosive outbreak in an unimmunized population even if there is only one laboratory-confirmed case in the population. The most vulnerable group are children. Effective disease surveillance activities remain the best tool for prompt detection of and response to outbreaks, particularly in populations where coverage rates for YF vaccine are not high enough to provide protection. These guidelines describe how to detect and confirm suspected cases of yellow fever. They also describe how to respond to an outbreak of yellow fever and prevent additional cases from occurring.
Yellow Fever Epidemiology
Yellow fever often occurs in Africa and South America. The epidemiology of yellow fever presents different challenges on each continent, even though it is caused by the same virus. In Africa, there has been an increase in the number of reported YF cases in Africa during the last five to 10 years WHO estimates that there are 200 000 cases annually and that 30, 000 deaths occur each year in 44 countries at risk, majority occur in sub-Saharan Africa. The increase was probably attributable to reduced coverage rates for YF immunization and to the neglect of mosquito control program. Based on this, the Eliminate Yellow fever Epidemics (EYE) strategy was developed by WHO to respond to the increased threat of yellow fever urban outbreaks with international spread.
