Yellow fever (YF) is an acute viral communicable disease transmitted by an 
arbovirus of the Flavivirus genus. It is primarily a zoonotic disease, 
especially the monkeys. Worldwide, an estimated 200,000 cases of yellow fever 
occurred each year, and the case-fatality rate is ~15%. Forty-five endemic 
countries in Africa and Latin America, with a population of close to 1 billion, 
are at risk. Up to 50% of severely affected persons from YF die without 
treatment. During 2009, 55 cases and 18 deaths were reported from Brazil, 
Colombia, and Peru. Brazil reported the maximum number of cases and death, i.e., 
42 cases with 11 deaths. From January 2010 to March 2011, outbreaks of YF were 
reported to the WHO by Cameroon, Democratic Republic of Congo, Cote d'Ivoire, 
Guinea, Sierra Leone, Senegal, and Uganda. Cases were also reported in three 
northern districts of Abim, Agago, and Kitugun near the border with South Sudan. 
YF usually causes fever, muscle pain with prominent backache, headache, shivers, 
loss of appetite, and nausea or vomiting. Most patients improve, and their 
symptoms disappear after 3 to 4 d. Half of the patients who enter the toxic 
phase die within 10-14 d, while the rest recover without significant organ 
damage. Vaccination has been the single most important measure for preventing 
YF. The 17D-204 YF vaccine is a freeze-dried, live attenuated, highly effective 
vaccine. It is available in single-dose or multi-dose vials and should be stored 
at 2-8 °C. It is reconstituted with normal saline and should be used within 1 h 
of reconstitution. The 0.5 mL dose is delivered subcutaneously. Revaccination is 
recommended every 10 y for people at continued risk of exposure to yellow fever 
virus (YFV). This vaccine is available worldwide. Travelers, especially to 
Africa or Latin America from Asia, must have a certificate documenting YF 
vaccination, which is required by certain countries for entry under the 
International Health Regulations (IHR) of the WHO.