Collaborative study for validation of a serological potency assay for rabies vaccine (inactivated) for veterinary use

European Pharmacopoeia (Ph. Eur.) monograph 0451 on Rabies vaccine (inactivated) for veterinary use describes an in vivo batch potency test that is based on the NIH test. This assay uses a large number of mice and results in a significant degree of suffering. In the interest of replacement, reduction and refinement of animal tests (3R) a serological potency assay for Rabies vaccine (inactivated) for animal use, developed and validated at the Paul-Ehrlich-Institut, has been assessed in a collaborative study organised by the EDQM (European Directorate for the Quality of Medicines & HealthCare). The goal was to demonstrate the wider transferability of the proposed assay and confirm its suitability. The study involved 13 laboratories and assessed 4 different vaccines from the EU market. Results of the study confirm that a limit test using a relatively small number of animals in a serological assay is possible, reproducible and reliable. The optimal number of animals per vaccine is product specific but may roughly be indicated to be between 8 and 10 for the products included in this study. Non-responders should be included in the analysis because they may reflect sub-potent vaccines. However, there may be a need to impose a maximum on the number of non-responders allowed for the reference vaccine as a monitor for assay validity. This assay provides a significant 3R improvement in terms of both the number of animals used and the amount of suffering entailed and provides a more reliable and reproducible assay format than the vaccination challenge assay. It also reduces the time required as compared to the vaccination challenge assay. It has been recommended to the Ph. Eur. group of experts 15V that this assay be included as an alternative to the batch potency assay in the Ph. Eur. monograph 0451.