Immunogenicity and booster efficacy of pre-exposure rabies vaccination

A multivariate analysis was used to identify factors influencing the immunogenicity of rabies vaccine and to assess the efficacy of booster injections in a cohort of 407 people monitored prospectively for 10 years after primary vaccination. Rabies vaccine (HDCV or PVRV) was injected by intramuscular route either on days 0 and 28 or on days 0, 7 and 28. All the participants received a booster injection on day 365. At the end of follow-up (year 10), 163 subjects had titers >0.5 IU/ml (group A) and 59 subjects had titers <0.5 IU/ml (group B: poor responders). The number of injections had a significant influence (P < 0.001) on the magnitude of the serological response to rabies vaccine, but the type of vaccine and the potency of the batches did not (P = 0.07 and P = 0.06, respectively). The difference between GMTs on day 365 and day 379 was significantly lower in group B than in group A (13 and 50.70 IU/ml, respectively; P < 0.001). In conclusion, our study confirms that the rabies pre-exposure vaccination protocol of three intramuscular injections significantly decreases the proportion of poor responders at 10 years. Moreover, our findings indicate that a routine booster injection at 1 year could significantly increase the levels and duration of antibody titers.