Researchers worldwide have been working to develop a universal flu vaccine, but no breakthrough has yet been achieved. FLUniversal is not "another costly universal flu project". It is an opportunity to create a genuine universal flu vaccine that will set the standard for rapid, efficient vaccine development, and generate know-how and tools to develop next-generation vaccines. We plan to exploit our increased understanding of molecular mechanisms of influenza infection and immunity to develop a vaccine effective against all flu virus strains. Our innovation uses genetically modified flu strains administered intranasally in a prime-boost regimen. This approach rapidly induces interferon and broadly cross-neutralising antibodies in the nasal passages and a systemic immune response directed to the conserved HA stalk. Proof of concept for universal protection was demonstrated in the ferret; we propose now to show proof of concept in humans. Previous clinical studies established safety and immunogenicity in humans. The strains are efficiently produced in Vero cells. FLUniversal's objectives align with the Expected Outcomes: comprehensive immunological assessment of preclinical models, development of a human challenge model, and assisting healthcare stakeholders’ decision-making about support for vaccine development. Consortium members’ world-leading expertise in preclinical models, clinical trials, immunology and validated assays will provide valuable insights on mechanisms of protection. Proposed clinical studies will provide crucial clinical proof of concept to advance the vaccine toward commercialisation.