Workshop report: Improving standardisation of rabies serology methods and procedures

Rabies is a viral disease transmitted primarily through bites or contact with saliva from infected mammals and annually causes approximately 70,000 human deaths worldwide. Rabies vaccines stimulate the production of rabies virus neutralising antibodies (RVNAs), and several assays are used to quantify their concentration. An RVNA threshold of 0.5 IU/mL, set in 1977, is used to determine protection in both humans and animals. In June 2024, an expert workshop was convened after the observation of declining RVNA geometric mean titres in response to 3 different human rabies vaccines, irrespective of vaccine manufacturer. Current challenges in rabies serology were discussed, particularly the need for assay standardisation and a subsequent reassessment of the 0.5 IU/mL RVNA threshold in humans. Key practical recommendations included improved methodological standardisation, rigorous quality control, and structured training to enhance inter-laboratory data comparability. The workshop participants recommend establishing an international working group to drive future validation efforts and support consistent interpretation of rabies serology results worldwide. • Rabies vaccines stimulate production of rabies virus neutralising antibodies (RVNA). • An RVNA serum titre of ≥0.5 IU/mL is accepted as serologic evidence of protection. • There is a need to reassess the 0.5 IU/mL threshold in humans. • There are known challenges to estimating RVNA levels. • Individual laboratories need to develop relevant processes to standardise testing.