Persistence and booster response of rabies antibodies among health care workers with multiple vaccinations.

Rabies is a fatal but vaccine-preventable disease. Health care workers (HCWs) in endemic areas may receive repeated rabies vaccination because of occupational exposure, yet data on long-term antibody persistence and booster response after multiple prior vaccine regimens remain limited. This study aimed to determine the rabies antibody profile of HCWs previously vaccinated with rabies vaccine. We analyzed 126 HCWs from the Research Institute for Tropical Medicine (RITM) and Muntinlupa Animal Bite Treatment Centers (ABTCs) in the Philippines. Vaccination records were reviewed, and booster doses consisting of 0.1 mL purified Vero cell rabies vaccine (PVRV) were administered intradermally on days 0 and 3. Pre- and post-booster rabies antibody levels were measured using the rapid fluorescent focus inhibition test (RFFIT). All HCWs vaccinated within the previous year retained pre-booster antibody titers ≥ 0.5 IU/mL. Participants who had received three or more prior rabies vaccine regimens also maintained protective pre-booster antibody levels within 3-5 years after the last vaccination. After booster administration, all participants achieved antibody titers above the protective threshold ≥ 0.5 IU/mL, regardless of prior vaccination history or time since last vaccination. Repeated rabies vaccination was linked to sustained antibody persistence, while previous vaccination history was associated with preserved booster responsiveness among HCWs. These findings suggest that, in addition to time since last vaccination, the number of prior rabies vaccine regimens may help inform about the persistence of protective antibody levels in previously immunized individuals.