Abstract The main goal of the parent award related this supplement is to develop and test in vivo novel vaccine candidates towards the development of a universal influenza vaccine. By employing computational protein design and high-throughput library screening methods, we aim to generate novel immunogens that preferentially elicit broadly cross-reactive antibodies against diverse influenza viruses. As part of the parent award, we proposed to engineer and test in vivo two hemagglutinin (HA) head-based immunogens with the goal of eliciting broadly immune responses that target the HA head trimer interface. This HA region is conserved across many influenza subtypes and is engaged by multiple broadly cross-reactive antibodies. We have already tested in mice the immunogenicity of two engineered HA head immunogens and found that they elicit antibodies that cross-react with multiple influenza subtypes, unlike the WT HA head template that they were based on. Based on these results, we request funds in this application to further optimize and test HA head-based immunogens for the elicitation of HA head trimer interface antibodies. This supplement will provide resources to test additional immunogens than those planned in the parent award, and will make available more biologically relevant animal models for in vivo immunogen testing through a collaboration with the Duke Regional Biocontainment Laboratory (RBL). The Duke RBL has developed multiple mouse and ferret viral challenge models with diverse influenza strains that will now become accessible to us through this supplement. This proposal will therefore augment the work of the parent award, by providing the resources to further develop and rigorously test in vivo HA head derived immunogens with the final goal of discovering a universal influenza vaccine.