Yellow fever vaccine Foundation to improve the vaccine from the "Asibi" strain, discovered that a favorable chance mutation in the attenuated virus had produced a highly efficacious strain that was named 17D. After field trials in Brazil, over one million people were vaccinated by 1939, without severe complications. For his work on the yellow fever vaccine, Theiler received the 1951 Nobel Prize in Physiology or Medicine. Only the 17D vaccine remains in use today. The outbreak of yellow fever in Angola in January 2016 has raised concerns about whether the global supply of vaccine is adequate to meet the need during a large
Arnold Theiler sickness with a combination of live virus and equine antiserum. This disease is now known to be caused by a pegivirus. Theiler was the first Director of the Onderstepoort Veterinary Research Institute, outside Pretoria. This institute under his leadership carried out research on African horse sickness, sleeping sickness, malaria, East Coast fever ("Theileria parva") and tick-borne diseases such as redwater, heartwater and biliary. The University of Pretoria Faculty of Veterinary Science was established there in 1920 which enabled veterinarians to train locally for the first time. Theiler became the first dean of this faculty. He married Emma Sophie Jegge (1861–1951)