This is a randomized, observer-blind, trial in clinically-stable older adults. Up to 300
eligible older adults 60 through 80 years of age will be enrolled at a 1:1 ratio into
multiple dose/formulation treatment arms. Safety and immunogenicity data through Day 56 will
be used to select a vaccine candidate to potentially evaluate in a Part 2 study. Proportions
of subjects in various strata will not be pre-specified and the goal will be to achieve an
approximately equal distribution of subjects with these characteristics across the treatment
groups. Serology measures consistent with the study outcomes will be reported.