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Disease Information Sheets

Yellow Fever

Yellow fever is a viral disease spread by mosquitoes from monkeys to humans, between monkeys and between humans. It is found in tropical and subtropical areas of Africa and South America. Up to half of people who develop the severe form of yellow fever and who do not receive treatment die. Yellow fever can be prevented by vaccination. The vaccine is safe and very effective.

How common is it?

There are around 200,000 cases of yellow fever each year with 30,000 deaths. It is found in 44 endemic countries in Africa and South America. The number of cases has increased in recent years. This is thought to be due to increasing urbanisation, deforestation, declining immunity in the population, population movements and climate change.


Are travellers and/or expat workers at risk?

Yes. The mosquitoes responsible for transmitting yellow fever bite during the day. Unvaccinated travellers/expat workers are at the same or higher risk as the resident population.

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Areas with high (red) & low (pink) risk of yellow fever.

What is the illness?

Three to six days after being bitten by an infected mosquito, there is usually a sudden onset of fever, chills, severe headache, back pain, body aches, nausea, vomiting and weakness. Most people then improve, however in about 15% of cases a more severe form of disease subsequently develops involving haemorrhage, shock and organ failure. Up to half of people who develop this form of disease die.

How is it treated?

There is no specific treatment. Supportive care is required, and for severe disease this may involve intensive care.


How can it be prevented?

There is a safe and effective vaccine, providing good, long-lasting immunity. Some countries require a certificate proving you have been vaccinated before they will allow you in. If you cannot produce a certificate they may vaccinate you on the spot. You may not feel as confident in the health, safety and hygiene standards of the vaccine administration in some parts of the world as you would be at home. In order to be issued a valid certificate you must have it at an authorised Yellow Fever Vaccination Centre. Most GP surgeries and travel health clinics are authorised, but check with them when you make your appointment.


As well as vaccination, you should avoid mosquito bites. Mosquitoes that transmit yellow fever (and other viral diseases such as dengue) bite during the day. Use an effective insect repellent (DEET), long sleeves and trousers and clothing impregnated with permethrin. Stay in well-screened and/or air-conditioned rooms.


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