Throughout the 1940s and 1950s Australia had severe rabbit plagues. Fenner's work on the myxoma virus showed that initially it killed rabbits in 9 to 11 days and was 99.5% lethal. Under heavy selection pressure, the few rabbits that survived developed resistance, which meant that the pest was never completely eradicated, but their numbers were reduced. Prior to the release of the virus as a biological control for the rabbits, Fenner, Frank Macfarlane Burnet, and Ian Clunies Ross famously injected themselves with myxoma virus, to prove it was not dangerous for humans.