Wright's conception of the value of vaccine therapy was based on the accuracy of the opsonic index. When later the opsonic index was shown to be an unreliable guide, and since the immunologists had no better method for determining immune body formation, it was necessary in case vaccine therapy was to be continued that the clinician draw his own conclusions regarding the value of this method of treatment. Interpretation of results passed now from the hands of the laboratory worker to the clinician.
The application of any therapeutic measure to this group of diseases is fraught with considerable difficulties. Spontaneous recovery is the rule; the duration and intensity of the infection is so variable that it is extremely difficult to draw accurate conclusions regarding the value of any special line of treatment. In order to justify statements regarding curative agents, a large number of carefully selected controls must be studied,
MILLER JL. THE NONSPECIFIC CHARACTER OF VACCINE THERAPY. JAMA. 1917;LXIX(10):765–769. doi:10.1001/jama.1917.02590370001001