Rabies vaccine potency control: comparison of ELISA systems for antigenicity testing

Potency control of inactivated rabies vaccines for human and veterinary application is usually undertaken by vaccination-challenge tests (e.g. the mouse potency test). For practical and ethical reasons there is an urgent need to replace in vivo potency control procedures, at least in part, by reliable methods of in vitro potency testing. Quantitative ELISA systems for potency control were developed using monoclonal antibodies (MAbs) directed to the glycoprotein (GP) and to the nucleoprotein (NP) of the virus. Although immuno-capture and competition ELISAs for GP measurement had almost equal sensitivity (detection level GP < 0.1 IU), the competition data showed the best correlation with potency values when a panel of rabies vaccines for human use was tested (r = 0.88, n = 10). The NP values for this panel of vaccines in the competition system (detection level NP < 1 IU) also correlated well with potency values (r = 0.90, n = 10). The competition system proved to be best also with liquid adjuvanted veterinary rabies vaccines of LEP, PM, PV and SAD origin. The implementation of ELISA systems for potency control of rabies vaccines is discussed.