Emergencies preparedness, response

Yellow fever

Introductory level online course on yellow fever

12 March 2018 - An online course on yellow fever is available on the new OpenWHO learning platform and consists of interactive modules featuring video lectures, presentations and self-tests. The introductory course provides general information on yellow fever and is intended for personnel responding to outbreaks in complex emergencies or in settings where the basic environmental infrastructures have been damaged or destroyed. The course is available in English and French.

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.

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. Many people do not experience symptoms, but when these do occur, the most common are fever, muscle pain with prominent backache, headache, loss of appetite, and nausea or vomiting. In most cases, symptoms disappear after 3 to 4 days.

A small percentage of patients, however, enter a second, more toxic phase within 24 hours of recovering from initial symptoms. High fever returns and several body systems are affected, usually the liver and the kidneys. In this phase people are likely to develop jaundice (yellowing of the skin and eyes, hence the name ‘yellow fever’), dark urine and abdominal pain with vomiting. Bleeding can occur from the mouth, nose, eyes or stomach. Half of the patients who enter the toxic phase die within 7 - 10 days.

Yellow fever is difficult to diagnose, especially during the early stages. A more severe case can be confused with severe malaria, leptospirosis, viral hepatitis (especially fulminant forms), other haemorrhagic fevers, infection with other flaviviruses (such as dengue haemorrhagic fever), and poisoning.

Polymerase chain reaction (PCR) testing in blood and urine can sometimes detect the virus in early stages of the disease. In later stages, testing to identify antibodies is needed.

The yellow fever virus is an arbovirus of the flavivirus genus and is transmitted by mosquitoes, belonging to the Aedes and Haemogogus species. The different mosquito species live in different habitats - some breed around houses (domestic), others in the jungle (wild), and some in both habitats (semi-domestic). There are 3 types of transmission cycles:

1. Sylvatic (or jungle) yellow fever: In tropical rainforests, monkeys, which are the primary reservoir of yellow fever, are bitten by wild mosquitoes which pass the virus on to other monkeys. Occasionally humans working or travelling in the forest are bitten by infected mosquitoes and develop yellow fever.

2. Intermediate yellow fever: In this type of transmission, semi-domestic mosquitoes (those that breed both in the wild and around households) infect both monkeys and people. Increased contact between people and infected mosquitoes leads to increased transmission and many separate villages in an area can develop outbreaks at the same time. This is the most common type of outbreak in Africa.

3. Urban yellow fever: Large epidemics 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.

Good and early supportive treatment in hospitals improves survival rates. There is currently no specific anti-viral drug for yellow fever but specific care to treat dehydration, liver and kidney failure, and fever improves outcomes. Associated bacterial infections can be treated with antibiotics.

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