This is a randomized, controlled, observer-blind Phase 2 study which aims to confirm the optimal dose and formulation of VLA84 in healthy adults aged ≥ 50 years of age. The study will be enrolled in two age strata, subjects aged 50 - 64 years and subjects aged 65 years and older, in a 1:1 ratio.~500 subjects (thereof, 250 aged 50 - 64 years and 250 aged 65 years and older) will be randomized in a 3:3:3:1 ratio to receive either VLA84 75 µg w/o Alum, VLA84 200 µg w/o Alum, VLA84 200 µg w/ Alum (150 subjects each), or placebo (50 subjects). Vaccinations consist of two i.m. injections administered in close proximity to each other in the deltoid region at Day 0, 7 and 28, starting with the non-dominant arm and alternating arms between the vaccination days.~The study will investigate the immunogenicity and safety of VLA84 up to six months after the last vaccination, i.e. 210 days per subject. The study includes eight outpatient visits on days 0, 7, 14, 28, 35, 56, 120 and 210. Serum will be collected to assess humoral immunity at days 0, 7, 14, 28, 35, 56, 120 and 210.~The study is OBSERVER blind. This means only pre-defined study staff will be unblinded, e.g., staff responsible for IMP accountability, preparation and administration, monitor responsible IMP accountability, or safety staff in case of safety reasons. All other persons involved in study conduct will remain blinded.
Phase 2, randomized, observer-blind, placebo-controlled, multi-centric study including 4 parallel study groups.~500 Subjects (thereof, 250 aged 50 - 64 years and 250 aged 65 years and older) will be randomized in a (3:3:3:1) ratio to receive either VLA84 75 µg w/o (without) Alum, VLA84 200 µg w/o Alum, VLA84 200 µg w/ (with) Alum (150 subjects each), or placebo (50 subjects), as i.m. (intramuscular) vaccinations into alternating arms, on Days 0, 7 and 28