FIGURE 8.

Kaplan–Meier curves based on TTB end points demonstrate sterile immunity in group 3 vaccinees (homogenous triple-prime-boost pKarp47 regimen). The duration from ID inoculation of O. tsutsugamushi (challenge time point) until onset of bacteremia was termed TTB, and the onset of bacteremia served as the end point for a Kaplan–Meier survival analysis. A significant reduction of TTB was associated with plasmid DNA vaccine regimens of groups 3 (hazard ratio 0.073; p = 0.006) and 4 (hazard ratio 0.172; p = 0.032). The benefit in reducing bacteremia attributable to the homologous triple-boost regimen pKarp47(×3) was 2.35-fold higher than for the heterologous prime-boost pKarp47(×2)+Kp47/47-VRP vaccine candidate.