Six laboratories performed comparative bioassays in mice of the same 5 aluminum-precipitated toxoids sampled from current production of 5 manufacturers.Four of the toxoids were compared with the fifth toxoid as an arbitrary reference standard. Three doses of each toxoid were injected in groups of 12 mice each. The dose which produced median survival to a defined toxin challenge 14 days after immunization was chosen as the endpoint.Graded response measurements were obtained by scoring the degree of immunity in the individual mice as indicated by survival time and symptoms at survival.The intrinsic error of the assay was computed for each laboratory and the observed deviations in relative potencies were found to agree with the expectancy as established by the intrinsic error.Although the immunizability of the mouse populations varied up to 15 times between the laboratories, inclusion of the reference standard limited the inter-laboratory error of the assay to 60–160%, (95% fiducial limits).Comparative studies of the same toxoids in humans are being performed.
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