This study is a Phase 1, randomized, open-label study of the prime-boost vaccine candidates given in the prime-boost regimen previously demonstrated to have a high level of immunogenicity and immune durability: Day 0 prime (PIV) and Day 180 boost (LAV), and compare it with a previously untested schedule: Day 0 prime (PIV) and Day 90 boost (LAV) in order to define the potential tradeoff between potential immunogenicity, including cell-mediated immunity, and a more practical dosing schedule.