Yellow fever

What is yellow fever?

Yellow fever is a disease caused by a flavivirus that is transmitted by the bite of an infected mosquito. It gets its name from the yellowing of the skin and eyes (jaundice) that occurs when the virus attacks the liver. Yellow fever can be prevented by a vaccine.

What is my risk?

• Your risk can depend on many factors including your destination, the time of year (season), the length of your trip, and the types of activities you participate in.
• The risk is low for most travellers, but it may be higher for those who are going to areas of risk and who are staying for an extended period of time, visiting rural or jungle areas, or participating in outdoor activities such as camping, hiking, cycling or fieldwork.

How is it transmitted?

• Yellow fever is spread through the bite of infected mosquitoes, mainly the Aedes species in Africa and the Haemagogus species in South America.
• Mosquitoes that spread yellow fever typically bite during the daytime, particularly around sunrise and sunset.

What are the symptoms?

• Symptoms can take 3 to 6 days to appear.
• Initial symptoms usually include sudden onset of fever, chills, headache, joint and muscle pain, loss of appetite, abdominal pain, back pain, nausea and vomiting, fatigue, weakness and dehydration. Most patients recover after this stage.
• In severe cases, the disease can lead to shock, internal bleeding, jaundice (yellowing of the skin and whites of the eyes) and organ failure. This occurs in about 15% of patients, half of whom will die within 10-14 days.

Can yellow fever be treated?

There is no specific treatment for yellow fever, only supportive care to help relieve symptoms.

Where is yellow fever a concern?

Yellow fever is endemic (always present) in many tropical areas of Africa and South America.

Yellow fever can occur in urban areas when infected people travel from rural or jungle areas into highly populated areas, where the mosquitoes bite infected people and then spread the disease to uninfected people.

A list of countries where yellow fever transmission occurs (PDF format) is available from the World Health Organization (WHO).

Recommendations

Consult a health care provider or visit a travel health clinic, as early as possible (preferably six weeks or more) before you travel.

1. Get vaccinated
   • It is recommended that you get the yellow fever vaccine before you travel if you are going to a country:
     1. that requires proof of yellow fever vaccination to enter (on an International Certificate of Vaccination or Prophylaxis).
     2. where there is a risk of yellow fever.
   • In Canada, the vaccine is available only at designated Yellow Fever Vaccination Centres.
   • The single-dose vaccine against yellow fever is safe, effective and recommended for most people who are over nine months of age.
   • The vaccine is generally not recommended for pregnant or breastfeeding women, children under the age of nine months, adults 60 years and older (especially those who have not previously received the vaccine) and people with weakened immune systems.
   • If you are receiving the vaccine for the first time, be aware that it takes ten days for it to become effective (the International Certificate of Vaccination or Prophylaxis will only be valid ten days after the date of vaccination).
2. Protect yourself from mosquito bites, particularly around sunrise and sunset.