Single radial hemolyis Proportion of subjects with a Single radial hemolyis (SRH) area of ≥25 mm2 (seroprotection) after the second vaccination on Day 43 Proportion of subjects with SRH area of ≥25 mm2 after immunization in case of negative baseline sample (≤4 mm2) or 50% increase in SRH area if baseline sample is >4 mm2 (seroconversion).