Yellow fever is an acute viral haemorrhagic disease transmitted by infected mosquitoes. The "yellow" in the name refers to the jaundice that affects some patients. The virus is endemic in 47 countries across Africa and Latin America. According to the World Health Organization and Pan American Health Organization, yellow fever causes 200,000 infections and 30,000 deaths annually.
Large outbreaks of urban yellow fever occur when infected people introduce the virus into heavily populated areas with a high density of Aedes aegypti mosquitoes, and where most people have little or no immunity, due to lack of vaccination or prior exposure to yellow fever.
Thirteen countries in the Americas are considered to be at highest risk for yellow fever outbreaks, including Brazil and Colombia, where the World Mosquito Program works. While the urban transmission of yellow fever by Aedes aegypti has not been reported in Brazil since 1942, the risk of re-urbanisation of the disease remains, as these mosquitoes are found in most tropical and subtropical cities in the world and have been the main carrier of yellow fever in the past.
Safe and affordable, the yellow fever vaccine is the most important means to combat the virus - a single dose provides life-long immunity.
The World Mosquito Program’s Wolbachia method is helping to reduce yellow fever transmission, as well as other viruses transmitted by Aedes aegypti mosquitoes, such as dengue, Zika and chikungunya.