Rabies prophylaxis in man has long been a special problem when it involves particular groups of persons with unusual risks of repeated exposure, such as veterinarians, dog handlers, field naturalists, laboratory workers and those employed in endemic areas, where wild or domestic animal bites are an occupational hazard. In these groups repeated exposure formerly meant repeated treatment with vaccine of nervous tissue origin, thus increasing the possibilities of severe reactions to the vaccine, especially those involving the central nervous system. Now, however, there have become available 2 types of avianized vaccine (the duck embryo and the HEP chicken embryo vaccine), which, being almost devoid of encephalitogenic properties, may safely be used for the prophylactic immunization of man.

For such prophylaxis the schedule of immunization has ordinarily consisted of 3 doses of avianized vaccine given at approximately weekly intervals, followed in several months by a 4th or booster dose. Thus ANDERSON et al.[this Bulletin, 1960, v. 57, 899] administered duck embryo vaccine intradermally (0.2 ml. per dose) to 49 volunteers; 3 inoculations were given at intervals of 5 days, followed by a booster inoculation about 4 months later. Results of this trial showed 85% to have responded with antibody to the 3 primary inoculations and 96% to the booster dose; moreover, the average antibody titre after the booster dose was approximately 4 times that seen after the initial series of inoculations. Unfortunately, however, the results of other trials in which similar intradermal dosage schedules were employed proved to be anything but consistent, the antibody response having varied from 30% to 98% of those tested.