Potency testing of inactivated rabies vaccines using a serological method.

Batch potency testing of rabies vaccines could be done by challenge, measurement of serum response or antigen quantification. Here, we show the development of a serological test that was successfully validated for use in batch release. The serological test is based on serum neutralization (SNT). The correlation to the NIH challenge was demonstrated by batches passing respectively failing equivalently in the NIH and SNT. The SNT provides information on immunogenicity and exhibits several advantages to the NIH: 1) SNT uses many fewer animals for batch release. 2) SNT allows quantitative information on the individual serum response, in contrast to the "dead"/"alive" interpretation of the NIH. 3) SNT is quicker than the NIH and needs fewer working hours. 4) SNT avoids the highly disturbing intra-cerebral injection and suffering from rabies for mice and spares the staff the emotional stress of massively harming animals.

The rapid fluorescent focus inhibition test is a suitable method for batch potency testing of inactivated rabies vaccines.

The European Pharmacopoeia proposes two methods for potency determination of inactivated rabies vaccines for veterinary use: The first one is a classical mouse challenge test, which is imprecise, time-consuming, and causes severe distress to the test animals. Alternatively, the potency may be determined serologically by measuring the neutralizing antibody titers induced after vaccination of mice by using a rapid fluorescent focus inhibition test (RFFIT). Although this method is faster and less painful for the animals, it is not widely used yet, and only little data exist concerning the comparability of both methods. We have therefore performed a comparative study, in which we demonstrated a good correlation between the challenge test results and the mean titers determined by RFFIT. Furthermore, all vaccine batches failing the challenge test were also recognized as insufficient in the serological assay. This publication further describes the influence of different vaccine administration routes on the resulting antibody titers, and it proposes various modifications to the serological assay protocol which could improve its overall practicability. Finally, we recommend that the serological assay be used for the potency testing of inactivated rabies vaccines.