[1] Born in Pretoria, Theiler was educated in South Africa through completion of his degree in medical school.

That year, he moved to the United States to do research at the Harvard University School of Tropical Medicine.

[2] Theiler wanted to pursue a career in research, so in 1922, he took a position at the Harvard University School of Tropical Medicine in Cambridge, Massachusetts.

In 1926, they disproved Hideyo Noguchi's hypothesis that yellow fever was caused by the bacterium Leptospira icteroides.

It took until 1937, and more than 100 subcultures in chicken embryos, for Theiler and his colleague Hugh Smith to obtain an attenuated strain, which they named "17D".

Theiler's team rapidly completed the development of a 17D vaccine, and the Rockefeller Foundation began human trials in South America.

Between 1940 and 1947, the Rockefeller Foundation produced more than 28 million doses of the vaccine and finally ended yellow fever as a major disease.