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Yellow fever

NHS Direct Online Health Encyclopaedia


Yellow fever is viral disease that occurs mainly in Africa and the Americas. It is passed to humans through the bites of mosquitoes carrying the disease, usually during daylight hours. The symptoms of yellow fever can be severe, and it is possible to die from the disease.

Large areas of Africa and the Americas, including parts of the Caribbean are at risk, and travellers to those areas are strongly advised to have a vaccination for yellow fever around ten days before they travel.


Once in your system, the virus has no effect for three to six days. This time is called the incubation period. Two phases of the disease can then follow: the ‘acute’ first stage and the ‘toxic’ second stage. Symptoms of the acute stage include fever, headache, shivers, muscle pain, nausea and vomiting, and an unusually slow pulse. Three or four days later these symptoms normally disappear.

However, within 24 hours of these symptoms passing, around 15% of people who have been infected with this virus then develop the toxic phase. If this happens, the symptoms include fever, yellow skin (jaundice, as a result of damage to the liver), abdominal pain, and vomiting. Bleeding can occur from the mouth, nose, eyes and/or stomach – blood can then also be seen in the vomit and faeces. The kidneys can also be affected, sometimes leading to kidney failure.

Between twenty and fifty per cent of people who enter this toxic phase of yellow fever die within ten to fourteen days. Those who recover do not generally suffer major organ damage, and are then immune to the disease for life.


Yellow fever is caused by a virus called the flavivirus.  It is passed on by the bite of a type of mosquito known as Aedes aegypti. 

First, the mosquito becomes infected by biting an animal or human with the virus.  It can then pass it on to any other animals or humans that it bites.  Once it is infected a mosquito remains a source of danger throughout its life.

It is thought that the virus is widespread amongst the monkeys that live in the tops of trees in the jungle (the jungle 'canopy') in some parts of Africa and America. 

Occasionally, an infected mosquito passes the disease on to a someone in the jungle (eg a forestry worker) who can then act as a source of infection when they return to their own community.


There is no specific treatment for yellow fever. However effective medical care can provide comfort, and many of the symptoms can be eased. For example, a fever can be treated with paracetamol. Intensive care may be beneficial for those who become seriously ill.


The best way to prevent yellow fever is to have the vaccination at least ten days before travelling to an ‘at risk’ area, to allow the immunity to develop in your system. It is a safe and very effective vaccination. One dose of the vaccine provides immunity for ten years, and sometimes for life. It is advisable to have a booster dose every ten years if you are still at risk.

Severe reactions to the vaccine are rare, however some people do experience mild side effects, such as headache, aches in the muscles (and sometimes at the site of the injection), or a slight fever. These symptoms usually fade after about a week.

People who should not have a vaccination for yellow fever include;

  • those with an affected immune system, for example if you are receiving chemotherapy or radiotherapy treatment,
  • women who are pregnant,
  • children under nine months old, and
  • those with an egg allergy (the vaccine contains small amounts of egg).

If you are planning to travel to an area where yellow fever is present, always consult your GP

© Queen's Printer and Controller of HMSO, 2005

Crown copyright material is reproduced with the permission of the controller of HMSO and the Queens Printer for Scotland



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