Prophylactic immunization of humans against rabies by intradermal inoculation of human diploid cell culture vaccine.

The antirabies human diploid cell vaccine produced by 1'Institute Merieux, Lyon, France, was administered intradermally to 35 high-risk volunteers using 0.2-ml amounts and various immunization schedules. Three groups never before vaccinated against rabies developed virus-neutralizing antibodies, the titer of which was dose dependent. A single injection stimulated the formation of antibodies. Four inoculations induced the highest antibody levels and the longest persistence of antibody. The administration of a single intradermal booster inoculation was sufficient, even in the case of low-persisting antibody, to elicit a rapid increase of antibodies to high levels. A primary inoculation course of two injections induced a sufficient antibody level which, in case of exposure, could apparently be rapidly elevated by a 0.2-ml intradermal booster inoculation. Adverse side reactions were observed in 7 of 14 individuals after a 1- or 1.5-year intradermal booster inoculation. We therefore suggest that the intramuscular and subcutaneous routes continue to be used for primary vaccinations and that the highly effective intradermal route be restricted to booster inoculations. This is the first long term study of this vaccine and should be a guideline for the pre-exposure treatment of high-risk personnel.