Yellow fever is an infection caused by the yellow fever virus. It has caused large epidemics in Africa and the Americas. The infection causes a wide range of disease such as high fever, bleeding into the skin, and necrosis (death) of cells in the kidney and liver, and even death. Although an effective vaccine has been available for 60 years, the number of people infected over the last two decades has increased and yellow fever is now a serious public health issue again.