High rate of insufficient antibody titers after single-day immunization with human diploid-cell-strain vaccine against rabies.

We examined the possibility of simplifying the currently recommended immunization schedule against rabies. Four groups of 11 healthy volunteers were each immunized with either one, two, four, or eight doses of 0.1 ml human diploid cell vaccine (HDCV) intradermally on 1 single day. Antibody titers in serum were determined using a rapid fluorescent focus inhibition test. Geometric mean antibody titers 10, 30 and 90 days after immunization were all greater than 0.5 IU/ml, which is considered protective. A dose-proportional increase in the geometric mean antibody titer was observed for all four groups. However, at each dose level, at least 1 of the 11 volunteers on day 30 and 2 of the 11 volunteers on day 90 had insufficient antibody titers less than 0.5 IU/ml. Single-day immunization against rabies with HDCV vaccine cannot be recommended because of the unacceptably high failure rate.