Use of the antibody assay in immunized mice for the determination of rabies vaccine potency.

At present, the NIH potency test is the most widely used method for determining the potency of rabies virus vaccines. The drawbacks of this test are well known and include significant test variability as well as the use of an unnatural challenge route. The antibody assay in immunized mice involves the assay of sera from mice immunized with serial dilutions of rabies vaccine. The amount of antibody in the sera is expressed in International Units per ml (IU/ml). Sera from identical dilutions of different vaccines are compared for potency with serum from the same dilution of U.S. Reference Rabies Vaccine. A "unit ratio" is calculated by dividing the serum potency value for the test vaccine by that for the reference vaccine at each dilution tested. This unit ratio may then be compared to the antigenic value generated by the NIH test performed on the same vaccines. In this study, results are reported for both duck embryo and human diploid cell culture vaccines using the Serum Neutralization Test in mice as well as the Rapid Fluorescent Focus Inhibition Test to assay the antisera. Correlations are presented between the unit ratio and antigenic value for all vaccines tested. Also, practical applications and limitations of the test are discussed.