A report on the laboratory assays carried out at the Lister Institute of Preventive Medicine on the typhoid vaccines used in the field study in Yugoslavia.

The results of the laboratory assays of the Yugoslav typhoid vaccines used in the field trials at Osijek are disappointing when compared with the results of the field trials.The tests carried out at the Lister Institute in England, the Central Institute of Hygiene in Zagreb, Yugoslavia, and the Walter Reed Army Institute of Research in the USA indicate that, except for the agglutination tests for H antigen, there is little or no demonstrable difference in the potency of the two Yugoslav vaccines in either active immunization tests or passive protection tests.Although only a relatively small number of assays were carried out using the intracerebral route of challenge, the results indicate that there is no advantage in this method over the more usual intraperitoneal route. Since there was a difference between the potency of the vaccines in the field trails, it must be concluded that the mouse is not a suitable animal for typhoid assay or that the proper way of testing the mouse has not yet been found. The great variation in detail in nominally identical tests made in different laboratories and the differences in the results emphasizes the essential importance of at least one common assay, identical in detail between collaborating laboratories, in a study of this kind.