Part II will evaluate the safety, tolerability, and immunogenicity of HA-F A/Sing vaccine in prime-boost regimens. Subjects will be stratified by age and randomized equally into Groups 3 and Group 4 as shown in the vaccination schema. In Group 3, subjects will receive DNA A/Sing vaccine via PharmaJet Needle-Free Injector on Day 0 and HA-F A/Sing vaccine via needle and syringe on Week 16. In Group 4, subjects will receive HA-F A/Sing vaccine via needle and syringe on Day 0 and Week 16.