The Nobel Prize season is upon us once again. Are you aware that only one person has ever received a Nobel Prize for developing a vaccine? The 1951 Nobel Prize for medicine went to Max Theiler, a South African physician, for the development of a vaccine against yellow fever.

Yellow fever seems like a disease from the history books, but each year there are still about 200,000 cases resulting in about 30,000 deaths around the globe.

The yellow fever virus is spread by mosquitoes. Mosquitoes catch the virus by biting infected humans or primates. Once in the mosquito, the virus multiplies and ends up in the mosquito’s saliva. The virus is transmitted to people when bitten by the infected mosquito.

Symptoms develop three to six days after the bite and commonly consist of fever, muscle pain, headache and nausea or vomiting. In most cases, symptoms disappear within four days. In a small fraction, a second phase occurs with the fever returning along with major injury to the liver and kidneys. The liver damage results in jaundice, the yellowing of the eyes and skin, for which the disease is named. Bleeding may occur from the eyes, nose, mouth or stomach. About half of the people who enter this second phase die within two weeks.

Although yellow fever is a disease of the tropics and subtropics, there were outbreaks in the United States. The virus was introduced into our country through the slave trade.

One of the most severe outbreaks occurred in August through November 1793 in Philadelphia. It resulted in more than 5,000 deaths. The last major outbreak was in New Orleans in 1905. Yellow fever was eliminated from the United States by draining swamps and using pesticides such as DDT to control the mosquitoes.

Theiler found yellow fever virus grown in mouse brains and chick embryos sometimes mutated. Some of the mutations resulted in worse disease in animals while other mutations resulted in very mild disease. He found one mutation that caused mild disease was stable.

In other words, the mutant almost never regained its capability to cause severe disease. The mutant virus was tested in humans to see if it could be used as a vaccine. It was found to be remarkably safe and effective. More than 600 million doses of this vaccine have been given over the last 80 years.

Yellow fever vaccination is recommended before travel to the majority of countries in South America and Africa. One dose of the vaccine provides lifelong protection. Some African countries require travelers to have an International Certificate of Vaccination or Prophylaxis. The requirement is to keep travelers from introducing yellow fever into disease-free areas, especially crowded urban settings.

Many think that in the next few years, another Nobel Prize will be awarded for vaccine development. The visionary groundwork that made the Pfizer and Moderna COVID-19 mRNA vaccines possible was laid by Drs. Katalin Kariko and Drew Weissman over the last 20 years. Certainly, these two are deserving of such an honor.

Vaccine Smarts is written by Sealy Institute for Vaccine Sciences faculty members Drs. Megan Berman, an associate professor of internal medicine, and Richard Rupp, a professor of pediatrics at the University of Texas Medical Branch. For questions about vaccines, email vaccine.smarts@utmb.edu.

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