The caption under the video is not quite correct, as Dr. Salk only states that the live virus vaccine causes polio but state, or at least implies, that his killed virus vaccine does not. The curious ching is that he makes a distinction between live and killed viruses when, acording to virology theory, viruses are not alive to begin with. What is not covered in this video is the fact that neither he nor any other virologist actually isolated any virus but rather dealt only with cultures from samples in which cells died and a virus was assumed to be the cause. Also, no vaccine is actually made from a virus that has been isolated but rather are made from the same culture method in which they merely claim a virus is present.