Vaccine equivalency, booster administration, and animal import decisions are based in part on the level of rabies virus neutralizing antibody (RVNA) in serum. The RVNA level 0.5 IU/mL is recognized by the World Health Organization to represent an adequate response to vaccination. This cut-off value was selected after expert review of serum neutralization testing (SN) of clinical trial samples. Other methods are currently or can be employed to measure rabies vaccine response. Commonly the same cut-off value, 0.5 IU/mL, is applied to provide information on which medical decisions are made. Studies have shown that although enzyme-linked immunosorbent assay (ELISA) and SN results are correlated, exact comparison cannot be ensured.