The BCG Vaccine Is First Given Against Tuberculosis

During the late nineteenth century, medical researchers sought to determine whether bovine tuberculosis could provide protection against human infection, drawing inspiration from earlier smallpox immunization techniques. In 1882, Robert Koch initially regarded human and bovine tuberculosis as identical. By 1895, Theobald Smith presented evidence distinguishing the two forms, a differentiation that Koch formally recognized in 1901 when separating Mycobacterium bovis from Mycobacterium tuberculosis. Early Italian human trials using virulent bovine bacteria proved disastrous, confirming that the bovine strain was fully capable of causing severe disease and requiring researchers to find a way to weaken the organism safely.

In 1908, physician and bacteriologist Albert Calmette teamed with veterinarian Camille Guerin at the Institut Pasteur de Lille to cultivate a less virulent form of the bacillus. Observing that a culture medium containing glycerin, bile, and potato reduced the virulence of the bacteria, the two scientists embarked on a long process of serial subculturing. Their subculturing continued through the German occupation of Lille during World War I, and by 1919, after about 230 subcultures, the strain no longer caused progressive tuberculosis in guinea pigs, rabbits, cattle or horses. This attenuated live bovine strain came to be known as Bacillus Calmette-Guerin, or BCG.