The sensitizing effect of various typhoid vaccines as revealed under experimental conditions.

Typhoid vaccines, both heat-inactivated vaccines prepared in liquid and solid media and alcohol-inactivated dry vaccines, frequently possess sensitizing properties. Heat-inactivated vaccines prepared in liquid media have higher sensitizing activities than those prepared in agar and alcohol-inactivated vaccines grown in liquid media under aeration.By inducing a Shwartzman phenomenon in rabbits, it is possible to characterize the sensitizing activity of each vaccine lot, and of its components, in comparison with a reference vaccine. The sensitizing activity of the supernatant fluid is as high as that of the whole vaccine but the washed microbic cells have a low activity. There is a marked correlation between the immunogenic activity, the toxicity and the sensitizing properties of the whole vaccine and its components-supernatant fluid and washed cells.Minimum requirements for permitted amounts of toxicity and sensitizing activity of typhoid vaccines can be formulated only after further information is obtained on the correlation between data from laboratory tests and assays of toxicity of vaccines in human subjects.