A co-operative evaluation of test systems used to assay tuberculosis vaccines.

The results of research on the immunogenicity of experimental mycobacterial vaccines are characterized by a remarkable lack of agreement about which substances are most immunogenic. The disagreement has usually been attributed to the differences in the methods of preparing the vaccines. An alternative hypothesis is that the conflicting results are a product of the different methods used to assess the potency of the vaccines.To determine if the method by which a vaccine is tested is a major factor contributing to the disagreement, an experiment was conducted in which a series of five different vaccines was distributed to each of nine participating laboratories. Each investigator evaluated the potency of the vaccines in one or more animal models of his own choosing. This in effect held the method of vaccine preparation constant while permitting all other variables to change.The ranking of the five vaccines was random, thus demonstrating that the method by which a vaccine is tested influences the apparent potency of a vaccine. These results cast doubt on the conclusions about the relative potency of tuberculosis vaccines evaluated by different methods.