Group 7A (Phase 1B extension) for Flu (MER4101 Trial)

The purpose of this study is to evaluate the safety, tolerance, and immunogenicity of MAS-1-Adjuvanted seasonal inactivated influenza vaccine (IIV) (MER4101) with hemagglutinin dose escalation compared to non-adjuvanted comparator IIV standard dose (SD) in healthy adults and high dose (HD) IIV in ambulatory elderly subjects. Hypothesis: Reduced HA dose IIV formulated in MAS-1 adjuvant (MER4101) has been shown under Phase 1A to be safe, tolerable and demonstrated a more robust and durable immune response to IIV over 6 months post-vaccination in healthy young adults 18 - 49 years of age compared to SD IIV. Under phase 1B, the 9 µg/HA dose of IIV in 0.3 mL MAS-1 was safe and well tolerated and immunogenically comparable to or better than 60 µg/HA HD IIV control over 3 to 6 months post-vaccination than HD IIV control. It is anticipated that the increased total dose of 15 µg HA antigen administered concurrently to opposite arms in 2 doses of 7.5 µg/HA IIV in 0.25 mL MAS-1 adjuvant emulsion will be safe, well tolerated, and more immunogenic than 9 µg/HA IIV in MAS-1, and will be more immunogenic when compared to HD IIV control in adults who are 65 years of age and older with the potential to provide better protection throughout the influenza season.