Immunogenicity of Rabies Postexposure Booster Injections in Subjects Who Had Previously Received Intradermal Preexposure Vaccination

Background: Preexposure rabies vaccination is recommended using the full dose intramuscular or less expensive reduced dose intradermal method. The reliability of the reduced dose intradermal preexposure regimen is still controversial. The objective of this study was to determine whether it will mount a predictable accelerated immune response after a simulated rabies exposure. Methods: One hundred and thirty-eight veterinary students received intradermal or intramuscular preexposure vaccination using a potent batch of purified chick embryo rabies vaccine. They then received booster injections one year later. Results: Subjects who received intradermal rabies preexposure vaccination, using 0.1 mL of a potent tissue culture vaccine on days 0, 7, and 28, had a lower postexposure booster antibody response 1 year later than subjects given the preexposure series intramuscularly. A significant number showed an unsatisfactory early anamnestic response. Residual neutralizing antibodies, 1 year after the intramuscular preexposure series, were also significantly higher in the intramuscular than in the 0.1 mL dose intradermal group. However, all study subjects had antibody titers above the minimum recommended level of 0.5 lU/mL by day 14. Conclusions: We conclude that not all subjects who received an intradermal preexposure vaccine series may be fully protected during the first 5 days after an exposure. Rabies immune globulin, injected into bite wounds and followed by a complete postexposure vaccine series, may be indicated if such a patient experiences a severe rabies exposure.