Ignaz Semmelweis saved lives but was ignored for decades

In 1847, Hungarian physician Ignaz Semmelweis noticed that maternity wards staffed by medical students had mortality rates three times higher than those staffed by midwives. The difference was that students came directly from performing autopsies. He mandated handwashing with chlorinated lime solution and mortality dropped from 10% to under 2%. The medical establishment dismissed him — germ theory hadn't been established yet — and he died in an asylum in 1865, his work vindicated only after Pasteur and Lister's later discoveries.

Source: Semmelweis, Etiology, Concept and Prophylaxis of Childbed Fever (1861)