[Pre-exposure rabies immunization in occupational exposed milieu. A 5-year prospective and comparative study of...

Pre-exposure rabies immunization has been the object of numerous immunogenicity studies with cultivated cell vaccines. Several primary immunizations and booster injection schedules have been suggested. The purpose of the present study was to compare simultaneously the immunogenicities of two vaccines at 5 years and those of two primary immunization schedules with a booster injection at 1 year. We compared the vaccine prepared from Vero cell cultures (PVRV) versus the reference vaccine prepared from human diploid cell culture (HDCV). We also compared primary immunization with 2 injections (on days 0 and 28) versus 3 injections (on days 0, 7 and 28). This phase IV study was prospective, randomized and conducted on open cohorts, according to a factorial plan defining four modalities (HDCV 2, HDCV 3, PVRV 2, PVRV 3). The study involved 312 volunteers of both sexes, aged from 15 to 65 years and exposed to rabies by their profession. The vaccines were injected intramuscularly in the deltoid region. Immunogenicity was evaluated by staged titering of neutralizing antibodies, using immunofluorescence. Seroprotection levels and mean geometrical means of titers were compared. The 3 injections schedule proved to be significantly superior to the 2 injections schedule. No difference could be clearly elicited between the two vaccines. The worst results were obtained with PVRV 2, with a 68.3 percent seroprotection rate at five years; with the other modalities this rate was 93.1 percent or more. We therefore recommend the following procedure: primary immunization by 3 injections, with a booster dose at 1 year, particularly when PVRV is used. It seems that the seroprotection obtained in this manner would make it possible to envisage a booster injection every 5 years.