Phase 2 Phase 3 Phase 2 Phase 3 Phase 2 Phase 3 Sum Phase 2 Phase 3 Sum Day 1 Day 43 Day 1 Day 43 Placebo Vaccine 13 A seroresponse with at least a four-fold increase in post-injection HAI titers on Day 43 compared with baseline (Day 1) was achieved for 75.08% (95% CI: 69.94 to 79.74) of subjects in the Phase 2/3 combined 15 mcg vaccine group 3.1.1.3.