Emergencies preparedness, response

Yellow fever

Nigeria launches Yellow fever vaccination reactive campaign to contain outbreak in Ebonyi State

WHO/AFRO

7 September 2019 - The Federal Government, in collaboration with WHO, Gavi, the Vaccine Alliance and partners, is launching a yellow fever reactive vaccination campaign in three States to help control an expanding yellow fever outbreak in Nigeria identified in Ebonyi State. The vaccination campaign targets 1.6 million people.

Strengthening country capacity for yellow fever diagnostics

22 March 2019 - The International Conference on Re-emerging Infectious Disease (ICREID) was held on 13-15 March in Addis Ababa, Ethiopia, hosted by the African Centres for Disease Control at the African Union. The event included a well-attended symposium on yellow fever, entitled "Challenges in emerging infectious disease preparedness – the Yellow Fever case."

Sudan set to protect over 8 million people with its largest ever yellow fever vaccination drive

20 March 2019 – The Federal Ministry of Health, in collaboration with WHO, Gavi, the Vaccine Alliance, and UNICEF has launched a large-scale mass vaccination campaign in Sudan to vaccinate over 8.3 million people aged from 9 months to 60 years against yellow fever in the states of Blue Nile, Gezira and Sennar during 10–29 March 2019.

The campaign represents a crucial step in protecting a large portion of the population and reducing the risk of severe and deadly yellow fever outbreaks in the country.

Experts caution against stagnation of immunization coverage in Africa

WHO/AFRO

23 January 2019 - Global immunization experts attending the biannual Regional Immunization Technical Advisory Group (RITAG) meeting urged African countries to strengthen their routine immunization. Over the past five years, immunization coverage in sub-Saharan Africa has stagnated at 72%, exposing populations to vaccine-preventable diseases and outbreaks.

The immunization experts also emphasized the importance of increased domestic investment in disease surveillance and the need for community engagement to drive vaccine deployment during outbreaks.

Nigeria launches yellow fever vaccination campaign to stop outbreak in Edo state

WHO/AFRO

20 December 2018 – The Government of Nigeria with support from WHO and partners launched this week a yellow fever reactive vaccination campaign. More than 1.4 million people from 9 months to 44-years-old are expected to be protected in this seven-day campaign, which will use part of the 3.1 million doses provided by the International Coordination Group (ICG) on Vaccine Provision, funded by Gavi, the Vaccine Alliance.

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.


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Video: Yellow fever - facts and challenges

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This course provides a general introduction to yellow fever and is intended for frontline responders engaged in preventing and managing outbreaks. The course takes approximately 1 hour to complete.

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

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