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 the appropriate tools to combat the attack were more resistant than the control group. In this case, the simple act of forewarning of an attack was enough to resist the counterattitudinal persuasion. The second component, refutational preemption, is the cognitive part of the process. It is the ability to activate one's own argument for future defense and strengthen their existing attitudes through counterarguing (Pfau, 1997). Scholars have also explored whether other resistance processes might be at work, including affect. Refutational preemption provides specific content that receivers can employ to strengthen attitudes against subsequent change. This aids in the inoculation process