[Potency testing of veterinary vaccines, rabies vaccines as an example]

Vaccines which are produced commercially should be controlled with respect to their efficacy (potency) and their "harmlessness" to the recipient animal. The basis for any potency test is the protection test in the target animal species. When a vaccine has been shown to be capable of protecting a particular species from a certain disease, alternative methods for potency testing often can be developed. The justification of the latter is that experiments which analyze the protection are cost-intensive, require a large number of animals and give only a moderate degree of reproducibility. Methods such as protection experiments in laboratory animals, the induction of the substances responsible for protection (such as antibodies) in target or laboratory animals as well as with in vitro tissue culture systems, or the quantitative determination of the immunogens (the components of a vaccine which should be responsible for protection) may be used only if their results correlate with those obtained from protection experiments in the target animal species. Rabies glycoprotein has been implicated as the main agent responsible for the induction of protection against rabies. The higher the content of glycoprotein in a rabies vaccine, the greater will be the potential of the vaccine to induce protection against the disease. Analyses of the rabies glycoprotein content in vaccines can make use of a number of methods which have proven acceptable (the immunodiffusion test, the antibody binding assay and the ELISA). However, in veterinary medicine most vaccines are associated with an adjuvant - a substance which should amplify the immune response of an animal against a vaccine. Since the adjuvants and vaccines in such preparations are inseparable, the presence of an adjuvant in a vaccine reduces the applicability of many in vitro methods. Thus, the above mentioned methods and possibilities for their adaptation to the analysis of adjuvanted vaccines will be discussed.