Several important scientific and technological developments have originated in South Africa. South Africa was ranked 60th in the Global Innovation Index in 2020, up from 63rd in 2019. The first human-to-human heart transplant was performed by cardiac surgeon Christiaan Barnard at Groote Schuur Hospital in December 1967, Max Theiler developed a vaccine against yellow fever, Allan McLeod Cormack pioneered X-ray computed tomography (CT scan), and Aaron Klug developed crystallographic electron microscopy techniques. With the exception of that of Barnard, all of these advancements were recognised with Nobel Prizes. Sydney Brenner won most recently, in 2002, for his pioneering work in molecular biology.