Subjects (n Å 312) received either the human diploid cell rabies vaccine (HDCV) or the purified Vero cell rabies vaccine (PVRV) according to either two-injection (days 0 and 28) or three-injection (days 0, 7, and 28) primary regimens. They received a booster injection at 1 year. Rabies antibody levels were measured after the primary series and the booster and then each year for the next 10 years. The results confirm the superior long-term immunogenicity of the three-injection over the two-injection protocol. HDCV and PVRV in three doses were equally immunogenic. A booster injection at 1 year provides long-term seroconversion (titer §0.5 IU/mL). Antibody titers 2 weeks after the 1-year booster allowed prediction of long-term immunity. Good responders, with titers §30 IU/mL, were protected for at least 10 years. An algorithm for differentiation between good responders and poor responders with respect to vaccine booster strategies is proposed.Preexposure rabies vaccination allows persons who may be the data from the present study [16] demonstrated that the three-dose schedule is more immunogenic than two injections later exposed to rabies virus to be protected by only two postexposure doses of vaccine. A three-dose preexposure series is the given on days 0 and 28, included for comparative purposes. ln addition, our preliminary analysis confirmed the importance of standard one recommended by the World Health Organization (WHO) [1], but two doses were recommended in France and the booster injection at 1 year in maintaining immunity [16]. For high-risk groups at continuous exposure to rabies, such in the United Kingdom [2]. Since the development of cellculture vaccines, numerous efficacy and safety studies have as workers in diagnostic and research laboratories, the recommendation of all health authorities is rabies antibody measuredetermined the most efficient protocol to use for the primary series of preexposure vaccination [3 -5]. Residual immunity 1 ment every 6 months, by use of the rapid fluorescent focus inhibition test (RFFIT), to verify that protective levels (neutralyear after the completion of the primary series also has been studied, but to a lesser extent [6,7]. In contrast, few reports ization at a 1:5 dilution [13] or at a titer of §0.5 IU/mL [1, 17]) are maintained. For other groups at risk, such as veterinarians or on the persistence of immunity have been published [8,9], and the schedule of boosters thus far proposed is based on travelers to areas in which rabies is enzootic, the frequency of boosters when RFFIT testing is unavailable has been deterextrapolation. The first cell-culture rabies vaccine, the human diploid cell vaccine (HDCV), was introduced in 1975 and has mined arbitrarily; recommendations vary from once yearly to once every 3 years [1, 13,18]. The risk of hypersensitivity become the reference standard [4, 10 -13]. Studies of the efficacy of a vaccine cultured on Vero cells (the purified Vero cell reactions to frequent HDCV boosters [13], reluctance to have frequent blood sampling, a...
