Evaluation of a non-invasive, inhalational challenge method for rabies vaccine potency assay

• Intranasal versus intracranial challenge in the rabies vaccine potency assay.
• A dose–response curve was produced when the intranasal route was used.
• Sub-potent preparations can be detected when the intranasal route is used.
• Intranasal challenge may be an acceptable refinement for mice.

Veterinary rabies vaccines are essential for safeguarding the public from exposure to rabies virus, as vaccination of domestic animals provides a barrier between humans and wildlife reservoirs. Ensuring rabies vaccines are potent and effective is paramount in preventing human exposure to rabies virus. The National Institutes of Health (NIH) test, a mouse vaccination-challenge assay, is the most widely used and internationally recognized assay for potency testing of inactivated rabies vaccines, and it is currently considered the method of choice. In the NIH test, vaccinated mice are challenged by the intracranial (IC) route. The response to the IC challenge can be variable, which often results in invalid tests. In addition, the IC challenge-exposure raises animal welfare concerns. The objective of this study was to evaluate the intranasal route of challenge as a modification to the NIH test to reduce animal pain and suffering until harmonized requirements for in vitro testing of rabies vaccines are developed. Results confirm the intranasal route is an effective route of rabies challenge in mice. However, a valid challenge requires the use of a more concentrated inoculum, in comparison to the intracranial method.