Emergencies preparedness, response

Yellow fever

Meeting demand for yellow fever vaccines, a joint statement by WHO, UNICEF and Gavi

29 January 2018 - Vaccination is the most powerful known measure for yellow fever prevention: a single dose can provide life-long immunity at a cost of approximately US$1. Ensuring adequate vaccine supply is available to reach all those at-risk is a constant challenge and the main purpose of the Eliminate Yellow Fever Epidemics (EYE) Strategy partnership, steered by WHO, UNICEF and Gavi, the Vaccine Alliance.

Brazil launches world’s largest campaign with fractional-dose yellow fever vaccine

25 January 2018 - Brazil has launched a mass immunization campaign that will deliver fractional doses of yellow fever vaccine to residents of 69 municipalities in the states of Rio de Janeiro and São Paulo. The strategic plan for the campaign was developed with support from the Pan American Health Organization (PAHO) and the World Health Organization (WHO). It will be the world’s largest vaccination campaign, to date, using fractional doses of yellow fever vaccine.

Nigeria set to vaccinate 25 million people, its biggest yellow fever campaign ever


24 January 2018 – The Government of Nigeria, with support from WHO and partners, will launch a mass vaccination campaign on 25 January 2018 to prevent the spread of yellow fever. More than 25 million people will be vaccinated throughout 2018, in the largest yellow fever vaccination drive in the country's history.

The immunization plan is part of efforts to eliminate yellow fever epidemics globally by 2026.

Vaccination recommendations for travelers related to the current situation in Brazil


16 January 2018 - Since December 2016, Brazil is experiencing an upsurge of yellow fever virus activity. Considering the increased level of yellow fever virus activity observed across the state of São Paulo, the WHO Secretariat has determined that, in addition to the areas listed in previous updates, the entire state of São Paulo should also be considered at risk for yellow fever transmission. Consequently, vaccination against yellow fever is recommended for international travellers visiting any area in the state of São Paulo.

Update on yellow fever in Nigeria

21 December 2017 - Reports of yellow fever cases throughout Nigeria are escalating concerns about the risk of large, costly, and difficult-to-control outbreaks in urban areas requiring huge supplies of life-saving vaccines and increasing the potential for large-scale national and worldwide spread. Fears that the situation in globally connected Nigeria could soon mirror the massive 2016 outbreak in Angola, during which cases were exported to neighboring DRC and as far as China, are raising urgent calls for quick containment.

The EYE Strategy addresses three important global health agendas

EYE is a global and comprehensive long-term strategy that aims at ending yellow fever epidemics by 2026. Areas of work encompass management of global vaccine supply including an emergency stockpile, and country implementation and engagement for improving surveillance and outbreak control.

The EYE strategy is committed to the main global health agendas: Universal Health Coverage, the International Health Regulations and Strengthening Health Systems.

African countries endorse the Eliminate Yellow Fever Epidemics (EYE) Strategy

African health ministers meeting in Victoria Falls, Zimbabwe, for the 67th Session of the WHO Regional Committee have agreed on ten priority actions to guide countries on the elimination of the yellow fever epidemics by 2026.

This endorsement reflects the strong political commitment of African nations to controlling yellow fever as a whole region.

An updated strategy to Eliminate Yellow fever Epidemics (EYE) has been developed by a coalition of partners (Gavi, UNICEF and WHO) to face yellow fever’s changing epidemiology, resurgence of mosquitoes, and the increased risk of urban outbreaks and international spread. This global, comprehensive long term strategy (2017-2026) targets the most vulnerable countries, while addressing global risk, by building resilience in urban centres, and preparedness in areas with potential for outbreaks and ensuring reliable vaccine supply. Its strategic objectives, built on lessons learned, are:

1) Protect at-risk populations;
2) Prevent international spread;
3) Contain outbreaks rapidly.

Yellow fever is caused by a virus (Flavivirus) which is transmitted to humans by the bites of infected aedes and haemogogus mosquitoes. The mosquitoes either breed around houses (domestic), in forests or jungles (wild), or in both habitats (semi-domestic).

Occasionally, infected travellers from areas where yellow fever occurs have exported cases to countries that are free of yellow fever, but the disease can only spread easily if that country has mosquito species able to transmit it, specific climatic conditions and the animal reservoir needed to maintain it.

Once contracted, the yellow fever virus incubates in the body for 3 to 6 days, followed by infection that can occur in one or two phases. The first, "acute", phase 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 days.

However, 15% of patients enter a second, more toxic phase within 24 hours of the initial remission. High fever returns and several body systems are affected. The patient rapidly develops jaundice and complains of abdominal pain with vomiting. Bleeding can occur from the mouth, nose, eyes or stomach. Once this happens, blood appears in the vomit and faeces. Kidney function deteriorates. Half of the patients who enter the toxic phase die within 10 to 14 days, the rest recover without significant organ damage.

Yellow fever is difficult to diagnose, especially during the early stages. It can be confused with severe malaria, dengue hemorrhagic fever, leptospirosis, viral hepatitis (especially the fulminating forms of hepatitis B and D), other hemorrhagic fevers (Bolivian, Argentine and Venezuelan hemorrhagic fevers as well as other Flaviviridae such as the West Nile and Zika viruses) and other diseases, as well as poisoning.

Blood tests can detect yellow fever antibodies produced in response to the infection. Several other techniques are used to identify the virus in blood specimens or liver tissue collected after death. These tests require highly trained laboratory staff and specialized equipment and materials.

There are three types of transmission cycle:

1. Sylvatic (or jungle): In tropical rainforests, yellow fever occurs in monkeys that pass the virus to mosquitoes that feed on them. The infected mosquitoes bite humans entering the forest resulting in sporadic cases of yellow fever, usually in young men working in the forest (e.g. loggers).

2. Intermediate: In humid or semi-humid parts of Africa, small-scale epidemics occur. Semi-domestic mosquitoes (that breed in the wild and around households) infect both monkeys and people. Increased contact between people and infected mosquitoes leads to transmission. Many separate villages in an area can suffer cases simultaneously. This is the most common type of outbreak in Africa. An outbreak can become a more severe epidemic if the infection is carried into an area populated with both domestic mosquitoes and unvaccinated people.

3. Urban: Large epidemics occur when infected people introduce the virus into a densely populated area with a high number of non-immune people and Aedes mosquitoes. Infected mosquitoes transmit the virus from person to person.

There is no specific treatment for yellow fever, only supportive care to treat dehydration, respiratory failure, and fever. Associated bacterial infections can be treated with antibiotics. Supportive care may improve outcomes for seriously ill patients, but it is rarely available in poorer areas.

Yellow fever can be prevented through vaccination and mosquito control.

The yellow fever vaccine is safe and affordable, and a single dose provides life-long immunity against the disease.

Mosquito control can also help to prevent yellow fever, and is vital in situations where vaccination coverage is low or the vaccine is not immediately available. Mosquito control includes eliminating sites where mosquitoes can breed, and killing adult mosquitoes and larvae by using insecticides in areas with high mosquito density. Community involvement through activities such as cleaning household drains and covering water containers where mosquitoes can breed is a very important and effective way to control mosquitoes.

Technical information

General information

This page links all WHO information on yellow fever in Portuguese.

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Regional information on yellow fever