Hypothesis: Reduced hemagglutinin (HA) dose IIV formulated in MAS-1 adjuvant (MER4101) is safe, tolerable and immunogenic in healthy young adults 18 - 49 years of age compared to SD IIV and an optimal dose of HA formulated in MAS-1 adjuvant will be safe and immunogenic in adults who are 65 years of age and older compared to HD IIV (from Phase 1A, known to be 9µg of HA antigen).