WHO Consultation on DT potency assay and consistency

Overview

Dr. Griffiths noted that DT vaccines have been remarkably successful, but that there are recognized problems in standardization and control of potencies of D- and Ttoxoids, even with International Standards. There is no globally accepted approach to potency measurement. In 1979 WHO requirements included for the first time definite recommendations for minimum potency requirements of 30 IU for D and 40 IU for T, and in 1990 confidence limits were added to the Requirements. When consistency of production and testing has been established, the current WHO Requirements allow use of fewer animals and one-dilution assays with the approval of the national regulatory authority. Methods based on toxin neutralization in vivo or on validated in vitro methods are also allowed. Since 1990 there has been much work done on validation of in vitro assays and the potential effect of this work on requirements for vaccine batch release has been considered.

As a result of previous meetings and discussions a draft proposal for simplified lot release was prepared and has been widely circulated for comments. This has been well received in principle, but many technical issues need to be resolved and agreed. The aims of this meeting were to review progress towards the development of robust and standardized in vitro assays for antitoxin measurement, to discuss potential solutions to outstanding technical issues related to the proposal for simplified lot release, and to consider steps which may advance the aims of assay simplification and harmonization.