Yellow fever is an acute viral haemorrhagic disease transmitted by infected mosquitoes. The illness can cause bleeding problems. It is called yellow because it makes the skin and the eyes yellow in color, like jaundice.

There is a vaccine which can stop the disease, but many people in Africa and South America are not vaccinated against it. The World Health Organization say that 200,000 people are made ill with yellow fever every year, and that 30,000 people die from it.