Long-Term Immunogenicity of Rabies Pre-Exposure Prophylaxis in Japanese Adult Travelers: Comparison of Dosing Regimens

Background/Objectives: Japan is a rabies-free country; therefore, pre-exposure prophylaxis (PrEP) is primarily recommended for travelers to rabies-endemic regions. However, no prior studies in Japan have assessed long-term immunogenicity after PrEP vaccination. Methods: This descriptive study evaluated the long-term persistence of rabies virus-neutralizing antibodies among Japanese adult travelers who had received PrEP. Neutralizing antibody levels were measured using the rabies rapid fluorescent focus inhibition test more than two years post-vaccination. Results: Among 97 participants, 86.6% remained seropositive, with a median interval of 8.5 years since vaccination. Individuals who received three or more doses had significantly higher geometric mean titers than those who received only two doses. A notable proportion of those vaccinated with PCECV-KMB, an older subcutaneous formulation, were seronegative after a long interval. Conclusion: Antibody levels were strongly influenced by the number of vaccine doses, with reduced persistence in those who received only two. If testing confirms sufficient titers, PrEP booster doses may not be needed. However, for individuals with only two doses, older vaccinations, or those given PCECV-KMB, a risk-based assessment is recommended—especially for travelers to rabies-endemic areas.