2013/2017 H7N9 Prime-Boost Interval

This is a Phase II trial designed to assess the safety, reactogenicity and immunogenicity of one or two doses of monovalent inactivated split influenza 2013 and 2017 A/H7N9 virus vaccines (2013 and 2017 A/H7N9 IIVs) administered intramuscularly at different dosages (3.75 or 15 mcg of hemagglutinin (HA) per dose), given with or without AS03 adjuvant, using different heterologous and homologous prime-boost vaccination schedules. Phosphate buffered saline (PBS) diluent may be used to achieve targeted dosages. This trial will enroll up to 180 males and non-pregnant females, 19 to 50 years of age, inclusive, who are in good health and meet all eligibility criteria and who are influenza A/H7 vaccine/infection naïve by medical history. Subjects will be randomly assigned to 1 of 6 treatment arms (30 subjects per arm) evaluating the interval between the priming (first) and boosting (second) doses and the presence of the adjuvant in the priming (first) and boosting (second) doses. The neuraminidase-specific antibody response and the neuraminidase content of the Inactivated Influenza Virus Vaccine will be determined using tests that are currently under development. Study duration is approximately 22 months with subject participation duration of approximately 18 months. The primary objectives of the study are: 1) to assess the safety and reactogenicity of 2013 and 2017 A/H7N9 IIVs given with or without AS03 adjuvant following receipt of each study vaccine; 2) to assess the serum hemagglutination inhibition (HAI) and neutralizing (Neut) antibody responses following receipt of the second study vaccine. The secondary objectives are: 1) to assess unsolicited non-serious adverse events (AEs) following receipt of each study vaccine; 2) to assess medically-attended adverse events (MAAEs), including new-onset chronic medical conditions (NOCMCs) and potentially immune-mediated medical conditions (PIMMCs), following receipt of each study vaccine; 3) to assess the kinetics and durability of serum HAI and Neut antibody responses following receipt of each study vaccine.