Antibody Response to a Human Diploid Cell Rabies Vaccine

An experimentally killed rabies virus vaccine prepared in a human diploid cell strain (WI-38)-Wyeth rabies vaccine (WRV)-was used by various injection schedules in two separate studies to define more closely in human volunteer subjects an effective vaccination schedule for pre- or postexposure immunization, particularly for donors of rabies-hyperimmune plasma. To permit valid comparisons between our results and those of other workers, antibody levels achieved were expressed in terms of international units (IU) per milliliter of serum. Antibody response of previously nonvaccinated persons were only modest after a single dose of WRV, never reaching a level higher than 0.80 IU/ml over a 56-day testing period. Moreover, antibody was not detected at 0.16 IU/ml before the 14th day, either after a single dose or after two doses given 3 days apart. The best response followed four doses of WRV given within 4 weeks. This schedule resulted in the highest rate of seroconversion to the >/=6 IU/ml antibody level required of potential rabies-immune plasma donors. Giving the first vaccine dose in aluminum hydroxide diluent did not enhance the antibody response. There was a definite suggestion in the various injection schedules that higher and more sustained antibody levels were reached when the interval between the first and second vaccine doses was longest. The greater immunogenicity of WRV as compared with duck embryo vaccine was best demonstrated by the fact that a single booster dose of duck embryo vaccine to previously vaccinated individuals resulted in only a sevenfold antibody rise during the following 56 days, whereas a booster dose of WRV elicited a 69-fold rise. Al(OH)(3) in the first dose of WRV had no effect, but the enhancing effect of a longer interval between vaccine doses was noted once again; 20 of 20 subjects who received three doses of WRV with 4 weeks between doses developed good levels of rabies antibody, and 19 exceeded 6 IU/ml.