BALB/c mice (8/group) were immunized i.d. with various vaccines, challenged with (A) 16 CFU at 49 days post-immunization (A, Experiment I) or with 31 (B) or 310 (C) CFU F. tularensis Schu S4 at 42 days (B, Experiment II) and monitored for signs of illness and death for 21 days. Mean Survival Day was calculated by dividing the sum of the surviving days of all mice by the total number of mice examined, with animals surviving until the end of the experiment given a survival time of 21 days, when the experiment was terminated. Survival curves between different groups were compared by log-rank test (Mantel-Cox) (Prism 6.04).