Yellow Fever

Factsheet

Key Facts

• 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.
• Symptoms of yellow fever include fever, headache, jaundice, muscle pain, nausea, vomiting and fatigue.
• A small proportion of patients who contract the virus develop severe symptoms and approximately half of those die within 7 to 10 days.
• The virus is endemic in tropical areas of Africa and Central and South America.
• 27 countries are at highest risk for yellow fever epidemics in Africa.
• The burden of yellow fever in Africa is estimated at 84,000–170,000 severe cases and 29,000–60,000 deaths annually. 
• In 2016, during the two-linked urban yellow fever outbreaks – in Angola and DRC – 965 cases were confirmed and around 400 people died. The epidemic created an urgent need for more than 28 million doses of yellow fever vaccines total, which exhausted the existing global vaccine supply. It also diverted public health authorities from tackling other public health issues with an impact on health systems. Additionally, 11 cases were exported to China.
• Since the launch of the Yellow Fever Initiative in 2006, significant progress in combatting the disease has been made in West Africa and more than 105 million people have been vaccinated in mass campaigns. No outbreaks of yellow fever were reported in West Africa during 2015.
• Large epidemics of yellow fever occur when infected people introduce the virus into heavily populated areas with high mosquito density and where most people have little or no immunity, due to lack of vaccination. In these conditions, infected mosquitoes transmit the virus from person to person.
• Yellow fever is prevented by an extremely effective vaccine, which is safe and affordable. 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 the vaccine is not needed. The vaccine provides effective immunity within 30 days for 99% of persons vaccinated.
• Good supportive treatment in hospitals improves survival rates. There is currently no specific anti-viral drug for yellow fever.

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.