Time interval for booster vaccination following reexposure to rabies in previously vaccinated subjects

Background: In rabies endemic areas, re-exposures to rabies are quite common and the incidence could be up to 15%. The recent guidelines of World Health Organization do not specify the duration of protection provided by previous pre- or post exposure prophylaxis. This often puts the treating physician in a dilemma in such cases of re-exposure.

Objective: Study the time interval between primary and booster vaccination in individuals who have taken previously a full course of either pre- or post exposure prophylaxis and are now re-exposed to rabies.

Methods: The data obtained through a literature search using Pubmed and advanced Google search along with data from in house clinical trials were used for analysis. Sixty-six vaccine cohorts spanning more than 27 years from 1983 to 2010 from six countries were studied. The duration of protection offered by previous vaccination was assessed by using a surrogate marker of adequate (> 0.5 IU per mL) rabies virus neutralizing antibody levels in the individuals vaccinated either by pre-exposure or post exposure regimens received by intramuscular or intradermal routes.

Results: The proportions of 2,795 subjects who had received prior post-exposure immunization and produced rabies virus neutralizing antibody levels of less than 0.5 IU per mL were 0.07% and 0.14% at the end of the first and third month post primary vaccination. All 577 subjects with previous pre-exposure vaccination had antibody responses above 0.5 IU per mL at the end of the first and third month post primary vaccination.

Conclusion: We concluded that it may be safe for up to three months after previous pre- or post exposure vaccination to not administer boosters to healthy subjects who have been re-exposed to rabies.