Immunization, yellow fever

A live attenuated (weakened) viral vaccine that is recommended for people traveling to or living in tropical areas in the Americas and Africa where yellow fever occurs. Because it is a live vaccine, it should not be given to infants or people with immune-system problems.

Yellow fever is an acute systemic (bodywide) illness caused by a virus called a Flavivirus. In severe cases, the viral infection causes a high fever, bleeding into the skin, and necrosis (death) of cells in the kidney and liver. The damage done to the liver from the virus results in severe jaundice which yellows the skin (provides the “yellow” in “yellow fever”).

The virus of yellow fever is transmitted in most cases by a bite of the Aëdes aegypti mosquito. (In a very few cases, the virus may be transmitted by a monkey bite.) Yellow fever once ravaged port cities in the United States, but no more. Today it is most common and concentrated in tropical areas of Africa and the Americas.

There is no cure for yellow fever. Prevention of the disease with the vaccine is most important. The vaccine is based upon classic medical research done under Dr. Walter Reed. When yellow fever broke out among U.S. troops in Cuba in 1900, Dr. Reed, a member of the Army Medical Corps, headed a commission of physicians on yellow fever. They discovered that the fever was transmitted by the Aëdes aegypti mosquito which breeds near houses (and also transmit dengue). Reed’s team later showed that the mosquito injected a virus that caused the dread disease. Sanitary engineers eradicated the mosquito and freed Cuba of yellow fever in 1902 (the year of Reed’s death from appendicitis).

The vaccine against yellow fever is also based on the work of Max Theiler. Dr. Theiler, from South Africa, worked at the Rockefeller Foundation (now the Rockefeller University) in New York. In 1929 Theiler contracted yellow fever (not an uncommon experience among those studying the disease) but recovered and became immune to it. The following year Theiler discovered that yellow fever can be transmitted to white mice, which are easy to handle and are available by the thousand at small cost. This was a critical finding for the production of the vaccine. In 1951, Max Theiler (1899-1972) was awarded the Nobel Prize in Physiology or Medicine “for his discoveries concerning yellow fever and how to combat it.”