Study Products: The investigational HA-F A/Sing vaccine, developed by the Vaccine Research Center (VRC), National Institute of Allergy and Infectious Diseases (NIAID), is composed of Helicobacter pylori non-haem ferritin with an influenza virus H2 hemagglutinin (HA) insert to form a nanoparticle displaying eight HA trimers from A/Singapore/1/57 (H2N2) influenza.