What approaches are being pursued for developing a universal influenza vaccine?

Universal flu vaccine aims to provide broad, durable protection against diverse strains, eliminating need for annual reformulation. Approaches: 1) Hemagglutinin stalk antibodies - target conserved HA stalk region rather than variable head; chimeric HA vaccines, headless HA constructs, computationally designed immunogens. 2) Neuraminidase targeting - NA is more conserved than HA head; anti-NA antibodies contribute to protection. 3) M2 ectodomain (M2e) - highly conserved but weakly immunogenic; fusion constructs and VLPs being developed. 4) Conserved internal proteins - NP and M1 for T-cell responses; important for cross-protection. 5) Mosaic/cocktail vaccines - combine multiple HA subtypes to broaden response. 6) Novel adjuvants - enhance responses to conserved epitopes. 7) mRNA platform - rapid antigen updating and potential multivalent approaches. Challenges: overcoming immunodominance of variable regions, correlates of protection less defined for stalk antibodies, T-cell immunity difficult to measure. NIH-funded trials ongoing; universal coverage remains 5-10+ years away.