Safety and Immunogenicity of Flublok Quadrivalent vs IIV4 in Adults 18-49 Years of Age

As the spectrum of influenza vaccines rapidly evolves to quadrivalent formulations with the
intention of offering broader protection to include both lineages of influenza B strains, it
is appropriate to transition Flublok from a trivalent to a quadrivalent formulation. The
demonstration of non-inferior post-vaccination Hemagglutination Inhibition Assay (HAI)
Geometric Mean Titers (GMTs) to antigens in the Flublok Quadrivalent formulation compared to
those of the matching antigens in a US - approved IIV4 is intended to support licensure of
Flublok Quadrivalent for the adult population for which Flublok trivalent is currently
approved. The comparison of safety and reactogenicity of Flublok Quadrivalent to that of
IIV4 is expected to confirm a similar safety profile.

Inclusion Criteria:

- Ambulatory, in good health or medically stable

- Able to understand and comply with planned study procedures

- Provide written informed consent

- Negative urine pregnancy test within 24 hours prior to vaccination (women of
child-bearing potential)

Exclusion Criteria:

- Prior serious or severe reaction to influenza vaccine

- Known contraindication to either study vaccine

- Receipt of any other influenza vaccine within 180 days prior to enrollment

- Plan to receive another licensed influenza or other vaccine during the duration of
this study

- Receipt of any significant new diagnosis, medication (licensed or investigational),
or licensed vaccine within 30 days prior to enrollment in this study

- Underlying disease or therapeutic intervention that might adversely affect the immune
response

- Plans to participate in any investigation involving an investigational product during
this study.

- Pregnant, lactating or planning to become pregnant within 30 days of study vaccine.

- Any clinical or social circumstance that in the opinion of the investigator could
interfere with compliance with study procedures or interfere with the interpretation