AN ADAPTATION OF QUALITY CONTROL CHART METHODS TO BACTERIAL VACCINE POTENCY TESTING

Abstract

Biological assays on bacterial vaccines are subject to variation from so many sources that absolute values (E.D.50 ''s) and standard errors of such end-points often are of little aid in adjudging the true potency of successive lots of such products. Consequently, any simplified, statistically valid procedure which woild aid in differentiating between variation resulting from the testing procedure and that reflecting true differences in potency would be useful in a routine testing program. Quality control chart methods have been found widely useful in inspection and control of manufactured articles as a rapid means of detecting true variations in quality. The appln. of such control chart methods to the interpretation of potency tests on typhoid vaccine has been investigated. Estimates of the expected variation in determination of E.D.50 and relative potency values were obtained by preliminary expts. and control charts were established with limits based upon these findings. 40 lots of vaccine were then assayed along with a reference standard in a series of expts. and the results plotted on the established charts. Variation in the absolute quantities required for protection (E.D.50 ''s) was readily distinguishable from variation resulting from the testing procedure. Throughout the period of study, no variation in relative potency, beyond that expected from the assay procedure, was observed among the successive lots of vaccine tested. It is considered that control chart methods simplify interpretation of the results of such potency tests and permit early detection of progressive changes in potency.