J.C.Byrne, R.Levis, Division of Viral Products, CBER, FDA, Bethesda, MD 20892
We are currently working in a collaborative study to develop an alternative potency test for rabies vaccine products. A critical assay for rabies vaccine product release is the vaccine potency assay. The current test, the NIH potency test, is an animal immunogenicity assay. There are several difficulties with this test. First, due to the inherent variability of mice, there is a high degree of variation between test results. There is no way to control for this, and therefore large numbers of animals must be used. Second, the current test takes up to ten weeks to complete. This has an impact on the time required for release of product. Third, the current test requires the use of virulent rabies virus to challenge immunized mice. This causes extreme discomfort for the animals, requires highly trained personnel, and specialized containment facilities. The goals of our collaborative studies, results of which will be presented, are: identification of antibody reagents that recognize all vaccine strains and the development of an antibody binding assay which is reliable and consistent with vaccine potency. Ultimately, in collaboration with other regulatory agencies and manufacturers, we hope to develop a new in vitro assay that will replace the current test.