Yellow fever is a potentially fatal viral disease transmitted to humans by infected mosquitoes. It generally occurs only in Africa, South America and the Caribbean. Each year, there are about 200,000 cases of yellow fever, which cause 30,000 deaths, according to the World Health Organization (WHO).

People who live in certain regions of the world are at risk for yellow fever. In rare cases, tourists and visitors to other countries may contract yellow fever. However, affected nations require vaccination for yellow fever before a person is allowed into the country.

Symptoms associated with yellow fever can vary dramatically from case to case. They tend to appear between three and six days after a person is bitten by a mosquito. Some patients only experience mild discomfort, while others develop severe and even life-threatening complications.

Yellow fever may be difficult to diagnose in its early stages because symptoms are similar to those of several other illnesses (e.g., malaria, influenza). No specific treatment exists for yellow fever except for supportive care, such as replacing fluids.

Yellow fever vaccine provides the best protection against this infection for people who are at least 9 months old. This live virus vaccine causes the body to produce antibodies to the virus, creating immunity from the infection for a decade or more.

People can also lower their risk of contracting yellow fever by taking steps to help prevent the mosquito bites that transmit the illness. Finally, government efforts to control mosquito populations have been effective in reducing the incidence of yellow fever.