Abstract: Oral rabies vaccination (ORV) is an effective tactic for wildlife rabies control, particularly for containment of disease spread along epizootic fronts. As part of the continuing evaluation of the ORV program in free-ranging raccoons ( Procyon lotor) in the US, 37 raccoons from ORV-baited areas in Pennsylvania were live-trapped and transferred to captivity to evaluate protection against rabies in animals with varying levels of existing neutralizing antibodies, expressed in international units per milliliter (IU/mL). Among the 37 raccoons at the date of capture, 24% (9/37) of raccoons were seronegative (0.11-3 mo after vaccination) appeared to be a surrogate indicator of survival. Overall, we illustrated significant differences in the value of specific titers as surrogates for survival based on the timing of measurement relative to vaccination. However, survivorship was generally greater than 45% among animals with any detectable titer regardless of the timing of measurement. These findings suggest that lower titer cutoffs may represent a valid approach to measuring immunization coverage within ORV management zones, balancing both sensitivity and specificity for estimating herd immunity.
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