What are the consequences of having frequent rabies booster vaccinations

Background: Physicians, laboratory scientists, veterinarians and public health officers who have had several potential rabies exposures, are given repeated booster injections often over years. We have experienced that these groups occasionally have a decline in Rabies Neutralizing antibodies (NAbs) when given frequent booster injections. Objective: We compared the dynamics of NAb titers between volunteers following primary vaccination and volunteers who had received repeated booster injections after primary vaccination. Method: We studied subjects who had a previous post-exposure rabies vaccine series and then received an intradermal booster on days 0 and 3. Results: Subjects who had only the primary series and no prior boosters had higher geometric mean NAb titers than those who had received one or more prior boosters. Conclusion: We present hypotheses for this phenomenon and recommend further studies to elucidate mechanisms that might have clinical implications.