Yellow fever information sheet

  •  Yellow fever is an acute viral haemorrhagic disease transmitted by infected mosquitoes.
  • Up to 50% of severely affected persons without treatment will die from yellow fever.
  • The virus is endemic in tropical areas of Africa and South America.
  • The number of yellow fever cases has increased over the past two decades due to declining population immunity to infection, deforestation, urbanization, population movements and climate change.
  • There is no cure for yellow fever. Treatment is symptomatic, aimed at reducing the symptoms for the comfort of the patient.
  • Vaccination is the most important preventive measure against yellow fever. The vaccine is safe, affordable and highly effective. The vaccine provides effective immunity within one week for 95% of persons vaccinated.
Signs and symptoms
  • The incubation period is between 3 and 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.
Differential diagnosis
  • Yellow fever is difficult to diagnose, especially during the early stages.
  • It can be confused with severe malaria, dengue hemorrhagic fever, leptospirosis, viral hepatitis, other hemorrhagic fevers as well as poisoning.
  • There is no specific treatment for yellow fever, only supportive care to treat dehydration and fever.


  • Vaccination is the single most important measure for preventing yellow fever.
  • Serious side effects are extremely rare.
  • The risk of death from yellow fever is far greater than the risks related to the vaccine.
  • People who should not be vaccinated include:
    • children aged less than 9 months for routine immunization (or less than 6 months during an epidemic);
    • pregnant women – except during a yellow fever outbreak when the risk of infection is high;
    • people with severe allergies to egg protein; and
    • people with severe immunodeficiency due to symptomatic HIV/AIDS or other causes, or in the presence of a thymus disorder
  • Travellers must have a certificate of yellow fever vaccination. If there are medical grounds for not getting vaccinated, International Health Regulations state that this must be certified by the appropriate authorities.

Mosquito Control

  • As with malaria, mosquito control is vital until vaccination takes effect and for continued prevention while in a yellow fever endemic area. The risk of yellow fever transmission in urban areas can be reduced by eliminating potential mosquito breeding sites and applying insecticides to water where they develop in their earliest stages.