The effectiveness of intradermal pre-exposure rabies vaccination in an Australian travel medicine clinic

Background: The objective of the study was to assess the effectiveness of intradermal (ID) rabies vaccination and to determine whether any difference in response with age or gender exists. No published Australian data on the subject is available and controversy continues to surround the use of ID rabies vaccination for pre-exposure prophylaxis. Vaccinated travelers requiring postexposure treatment are sometimes considered unvaccinated. By confirming their immunity prior to travel, this problem may be avoided. Methods: The data was collected by retrospective analysis over 2 years at a specialized travel medicine clinic in Perth, Western Australia. The standard protocol is three ID injections of 0.1 mL, given on days 0, 7, and 28 with a booster after 12 months. The vaccine used was the Pasteur Merieux human diploid cell vaccine. Serology was performed 3 weeks after completion of the primary course or after a booster. Antibody levels were measured using the rapid fluorescent focus inhibition test, and levels of > 0.5 IU/mL were considered protective. Results: A total of 164 travelers were included in the study, of which 144 had completed the three primary ID doses, and 20 had received an ID booster after a previous primary ID course. The mean age was 34.75 years, and gender distribution was equal. The median time between vaccination and serology was 23 days. The antibody levels ranged from 0 to 50 IU/mL with a mean of 8.42 IU/mL. Three travelers had no detectable antibodies giving a seroconversion rate of 98.2%. No statistically significant correlation between age or gender and antibody levels was present. Conclusion: We have found that ID rabies vaccination is effective in a travel clinic with nurses experienced in the technique. The lower cost of ID rabies vaccination makes it accessible to a larger number of travelers. Further studies will be required to determine the duration of protection after ID vaccination and antibody response after postexposure boosters. We will continue to recommend ID rabies vaccination if there is sufficient time for serology to be performed and for results to be available prior to departure.