Evaluation of the single radial-immunodiffusion assay for measuring the glycoprotein content of rabies vaccines

The glycoprotein content of rabies vaccines containing the Pitman—Moore strain of rabies virus was measured by the single radial immunodiffusion assay and correlated with vaccine potency. The variability of this assay was 6·3% for a single vaccine lot tested over a one-year period. Using sera prepared against rabies virus glycoprotein from different strains of virus, the assay gave different values. These differences could be eliminated by using a homologous vaccine strain as an internal reference. Single radial-immunodiffusion values for Pitman—Moore vaccines correlated with the manufacturers' NIH potency assay, but required a mathematical transformation to convert values from one assay to the other. Single radial-immunodiffusion values for Street Alabama Dufferin and Flury-LEP vaccines did not correlate with NIH values. Modification of the single radial immunodiffusion technique and the feasibility of using this assay for the determination of rabies vaccine potency are discussed.