One-year immunogenicity kinetics and safety of a purified chick embryo cell rabies vaccine and an inactivated Vero cell-derived Japanese encephalitis vaccine administered concomitantly according to a new, 1-week, accelerated primary series.

Background: Conventional rabies pre-exposure prophylaxis (PrEP) and Japanese encephalitis (JE) primary series vaccination regimens each require up to 4 weeks to complete and, thus, may not be feasible for individuals who need these immunizations on short notice. This Phase 3b, randomized, controlled, observer-blind study evaluated the immunogenicity and safety of concomitant administration of a purified chick embryo cell culture rabies vaccine and an inactivated, adsorbed JE vaccine according to an accelerated (1 week) regimen when compared with the conventional regimens (4 weeks). This report describes the kinetics of immune responses up to 1 year after vaccination. Methods: A total of 661 healthy adults (18 to = 97% of subjects had adequate levels of rabies virus neutralizing antibody (RVNA) concentrations (>= 0.5 IU/ml) up to Day 57, with percentages of subjects with RVNA concentrations >= 0.5 IU/ml at Day 366 ranging between 68% in the Rabies + JE-Accelerated group and 80% of subjects in the Rabies-Conventional group. The Rabies + JE-Accelerated group revealed high JE neutralizing antibody titers at all-time points. At Day 366, the percentage of subjects with antibody titers indicative of seroprotection (PRNT50 titers >= 1:10) remained high across JE vaccine groups (86-94%). Conclusions: The accelerated PrEP rabies and JE vaccination regimens, once licensed, could represent a valid alternative in the short-term to currently recommended conventional regimens. The concomitant administration of these two vaccines does not compromise immune responses to any of the vaccine antigens particularly when aiming for short-term protection. Further evidence will clarify the need for and timing to administration of rabies vaccine booster doses in subjects primed with an accelerated PrEP regimen. (NCT01662440)