Markers of cell-mediated immunity after vaccination with an inactivated, whole-cell Q fever vaccine.

A clinical trial of Q fever vaccine in four South Australian abattoirs showed apparently complete protection against natural infection; however, only 50%-60% of vaccinees developed complement-fixing or immunofluorescent antibody after vaccination. Cell-mediated immunity to Coxiella burnetii antigens, as measured by an index of lymphoproliferative responses (LSI) of peripheral blood mononuclear cells, was therefore assessed. Eighty-five percent of 13 subjects with "low risk" of exposure to Q fever and with an initially negative LSI converted to a positive LSI after vaccination; conversion was noted nine to 13 days after vaccination, and positive values were obtained for at least 96 d. Only 35% of this group seroconverted. In a "high-risk" group (abattoir workers), higher rates of positive LSI (greater than 95%) and of antibody (50%-70%) were observed after vaccination; greater than 95% of vaccinees in this group, who had been vaccinated five years previously, had positive LSI values.