Part I Primary: To assess the safety, reactogenicity, and tolerability of the VAX125 vaccine delivered i.m. in a single dose regimen of dose levels of 0.1 µg, 0.3 µg, 1 µg, 2 µg, 3 µg, 5 µg, and 8 µg in healthy adults 18 - 49 years of age, inclusive.