Figure 3. Correlation between TNA titers and protection after two injections. Relationship between serological titer and protection of guinea pigs with a double vaccination serially diluted of rPA vaccine at a 4-week interval. After 4 weeks after the second vaccination, guinea pigs were challenged i.m with B anthracis H9401 spores. Each point in the group represents the average of duplicate determinations performed with pooled sera derived from 9 or 10 guinea pigs. TNA titers of serum samples from individual animals in each group were compared to the survival data of the animals (inset). Linear regression was performed using data from experimental cohorts with neutralizing-antibody titers of 1176 or less. The calculated R2 value is 0.96.
