A colorized structure of a prototype from an earlier trial for a universal flu vaccine, known as H1ssF_3928, at the NIH Clinical Center in Bethesda, MD. The vaccine nanoparticle is a hybrid of a protein scaffold (blue) and eight influenza hemagglutinin proteins arrayed on the surface (yellow). The hemagglutinin protein was specifically engineered to display antibody binding sites common to all human influenza subtypes. The 3D structure of the particle was determined by cryo-electron microscopy. Image courtesy of National Institute of Allergy and Infectious Diseases.