Yellow Fever

Factsheet

Key Facts

• Yellow fever is a mosquito-borne viral disease, primarily transmitted by day-biting mosquitoes.
• Twenty-seven African countries and 13 Latin American countries are classified as high-risk for yellow fever outbreaks. The potential for international spread to unaffected regions remains a global health security concern.
• A safe, affordable vaccine provides lifelong protection with a single dose.
• An estimated 67 000-173 000 severe infections and 31 000-82 000 deaths occur each year in Africa and the Americas, with most of the burden being in Africa.

Yellow fever is an epidemic-prone, vaccine-preventable disease caused by a virus transmitted by infected Aedes sp., Haemagogus sp. and Sabethes sp. mosquitoes. These mosquitoes breed in domestic, forest (sylvatic), and semi-domestic environments.

Due to its high-impact and potential for international spread, yellow fever poses a significant threat to global health security.

Yellow fever is a viral disease, found in tropical regions of Africa and the Americas. The "yellow" in the name refers to the jaundice that affects some patients. It principally affects humans and monkeys, and is transmitted via the bite of Aedes mosquitoes. It can produce devastating outbreaks, which can be prevented and controlled by mass vaccination campaigns.

Large scale outbreaks occur every 3 to 10 years in villages or cities in the absence of large scale immunization. Sporadic cases can occur regularly in endemic areas.

The incubation period of the virus is 3 to 6 days after a bite from an infected mosquito. About 15% of infections progress to fever and jaundice. While only the minority of cases are severe, case fatality rate may be 25% to 50% among patients with syndrome of haemorrhage, jaundice, and renal disease.

Vaccination is the most important preventive measure against yellow fever. The vaccine is safe, affordable and highly effective. A single dose of yellow fever vaccine is sufficient to confer sustained immunity and life-long protection against yellow fever disease and a booster dose of yellow fever vaccine is not needed. The vaccine provides effective immunity within 30 days for 99% of persons vaccinated.