The Herd Immunity theory was originally coined in 1933 by a researcher called Hedrich. He had been studying measles patterns in the U.S. between 1900-1931 (years before any vaccine was ever invented for measles) and he observed that epidemics of the illness only occurred when less than 68% of children had developed a NATURAL IMMUNITY to it. This was based upon the principle that children build up their own immunity after suffering with or being exposed to the disease. So the herd immunity theory was, in fact, about natural disease processes and nothing to do with vaccination. If 68% of the population were allowed to build their own natural defenses, there would be no raging epidemic.
Later on, vaccinologists adopted the phrase and increased the figure from 68% to 95% with NO SCIENTIFIC JUSTIFICATION as to why, and then stated that there had to be 95% vaccine coverage to achieve immunity. Essentially, they took Hedrich’s study and manipulated it to promote their vaccination programs.
Reference: (MONTHLY ESTIMATES OF THE CHILD POPULATION "SUSCEPTIBLE' TO MEASLES, 1900-1931, BALTIMORE, MD, AW HEDRICH, American Journal of Epidemiology, May 1933 - Oxford University Press).