BCG vaccine bacilli that seemed less virulent, and changed the course of their research to see if repeated subculturing would produce a strain that was attenuated enough to be considered for use as a vaccine. The BCG strain was isolated after subculturing 239 times during 13 years from virulent strain on glycerine potato medium. The research continued throughout World War I until 1919, when the now avirulent bacilli were unable to cause tuberculosis disease in research animals. Calmette and Guerin transferred to the Paris Pasteur Institute in 1919. The BCG vaccine was first used in humans in 1921. Public acceptance was slow,
Inoculation theory body to a weakened form of a virus—strong enough to trigger a response (i.e., the production of antibodies), but not so strong as to overwhelm the body's resistance. Attitudinal inoculation works the same way: Expose the receiver to weakened counterarguments, triggering a process of counterargument which confers resistance to later, stronger persuasive messages. This process works like a metaphorical vaccination: the receiver becomes immune to attacking messages that attempt to change their attitudes or beliefs regarding the initial threat. Inoculation theory suggests that if one sends out messages with weak counterarguments, an individual can build immunity to those messages and