NIH test, a problematic method for testing potency of inactivated rabies vaccine.

A critical review of the NIH test is given. The results of four studies are presented which show that in the case of purified chick embryo cell inactivated rabies vaccine there is a profound difference between the result after heterologous intracerebral challenge with the prescribed CVS strain and homologous challenge with the LEP-C 26 strain. CVS strains from various laboratories produced relatively uniform results following intracerebral administration. Two in vitro tests, the single radial immunodiffusion test and the modified antibody binding test were employed in the studies. The results are discussed and alternative procedures to the NIH test are recommended for future consideration.