The relative immunizing efficiency of diphtheria toxoid preparations.

The results of a survey of diphtheria toxoids from a number of countries in different parts of the world show that wide differences exist in the potency values of the preparations in use today. Samples received from 20 laboratories in 11 countries were found to have variations ranging from 0.24 to 45.4 times the potency of the Canadian reference standard-a 189-fold spread. Specific reference is made in the article to the different types of toxoid, such as purified toxoid, aluminium-phosphate precipitated (PTAP), alum-precipitated toxoid (APT), formal toxoid (FT), etc., and their relative potency values are discussed. The results of these assays underline the inadequacies of minimum requirement tests used in most countries and the need for more precise methods of control.