Yellow fever once ranked among the greatest of human afflictions, conquered attempts at colonial settlement and economic development, and caused epidemics with much suffering in towns and cities as far north as Boston and Swansea. The conquest of yellow fever began in 1900 with Walter Reed's decisive investigations that proved transmission of the virus by Aedes aegypti, expelled public fear and confusion about causation, and provided a practical recipe for combating the disease. By 1927, the yellow fever virus had been isolated. Within a decade, tests were generated for measuring human immunity, and the French neurotropic and 17D live, attenuated vaccines were developed. Although discovery of the jungle cycle of yellow fever transmission in 1935 dispelled hopes of ever eradicating the disease, widescale use of vaccines in the 1940s and systematic efforts to subdue Ae. aegypti brought yellow fever under control.