Democratic Republic of Congo 2016 © Dieter Telemans/MSF
One shot of a vaccine gives long-lasting immunity, but low coverage in parts of the world leads to periodic epidemics.
Yellow fever is a mosquito-borne acute hemorrhagic viral disease without a cure. It occurs mostly in sub-Saharan Africa but is on the rise in Central and South America. In 2015-16, during the largest outbreak in 30 years, our teams vaccinated over 1 million people in Democratic Republic of Congo.
vaccine dose
provides long-lasting immunity
people
at risk of infection globally
people
vaccinated by MSF in 2016
Yellow fever is transmitted through the daytime bite of infected female Aedes mosquitoes.
Large epidemics occur in regions without good vaccination coverage—often a sign of a failing health system. Outbreak risk is especially high when displaced people move into heavily populated areas with high mosquito density and where the disease is common.
Most infections show no symptoms or only mild illness three to six days after infection, with fever and sometimes headache, chills, back pain, fatigue, nausea, and vomiting.
About 15 percent of infections progress to a severe phase, with recurring fever plus jaundice due to liver damage, causing yellow eyes. Some patients develop abnormal bleeding, for example in the mouth, eyes, and gastrointestinal tract. Half of these patients die within 10 days.
Surviving the infection provides long-lasting immunity, and typically there is no permanent organ damage.
Vaccination is the best way to prevent infection and stop outbreaks. People can also protect themselves against mosquito bites by wearing long clothing and using repellents and insecticide-treated mosquito nets, where available. At the community level, control measures include eliminating stagnant water where mosquitoes breed, and spraying insecticide.
Yellow fever is difficult to diagnose because many of its mild, early flu-like symptoms resemble those of many other infections. So, more severe cases can be confused with severe malaria, poisoning, viral hepatitis, or certain other viral diseases. Yellow eyes, due to jaundice, help doctors diagnose late-stage disease.
Definitive diagnosis requires testing of blood samples at specialized laboratories, and is usually done only if a new outbreak is suspected. Once the first cases are confirmed as yellow fever, an outbreak can be reported.
There is no specific antiviral drug for yellow fever, but hospital-based supportive care can save the lives of some patients.
We have responded to yellow fever epidemics since the year 2000 in countries including Angola, Democratic Republic of Congo, Guinea, Sudan, Sierra Leone, Central African Republic, and Chad. We aim to control outbreaks through mass vaccination campaigns and community-wide insecticide spraying to kill the mosquitoes that spread the disease, and to provide care for people with severe cases. We also work to improve the reach of a limited vaccine stockpile, and to advocate for increased vaccine supply and better routine vaccination coverage.
Community action and health promotion are essential to explaining the disease, the role played by mosquitoes, and what should be done in terms of prevention.
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