GSK said it will begin a Phase 3 test of its mRNA seasonal flu vaccine candidate after a Phase 2 study showed higher immune responses than traditional flu shots. The move reflects continued confidence in mRNA immunogenicity for influenza as the company aims to generate late-stage evidence of efficacy and durability. GSK’s decision comes as the broader field seeks consistent performance across formulation variants and patient populations, where immune response metrics need to translate into clinically meaningful endpoints. If Phase 3 confirms the immunogenicity advantage, the program could strengthen mRNA’s position beyond its pandemic-era visibility and support further investment into next-generation flu vaccine platforms. For biotech decision-makers, the milestone reinforces that late-stage trial strategy is increasingly tied to formulation refinement and immunogenicity-quality comparisons early in development.