doi:10.4269/ajtmh.2009.09-0295 Copyright © 2009 by The American Society of Tropical Medicine and Hygiene

Yellow fever (YF) is a systemic disease caused by a mos-quito-borne flavivirus that is found in tropical South America and sub-Saharan Africa. 1 The incidence of YF is estimated at approximately 200,000 cases per year, 2 and case-fatality rates as high as 20–50 % have been reported. 1,3 Because no antiviral compounds effective against YF virus are available, preven-tion is the mainstay of the current armentarium against this public health scourge. The 17D live attenuated vaccine, which was developed by prolonged serial passage of wild-type YF virus in chicken embryo tissue, is highly effective against YF virus. In persons who are vaccinated for the first time, mild viremia not exceed-ing 10 2 plaque-forming units/mL occurs 3–7 days after immu-nization, but viremia does not occur with subsequent doses of vaccine. This vaccine provides long-lasting immunity and has