GSK said it will begin a pivotal Phase 3 trial for its mRNA seasonal influenza vaccine after a Phase 2 study showed higher immune responses than traditional flu vaccines. The move positions the company to compete in mRNA flu as the next wave of late-stage contenders seeks differentiation through immune breadth and durability. The Phase 3 program is expected to be launched this month, following GSK’s reported success in inducing stronger immune responses in the Phase 2 setting. GSK’s strategy includes newer formulation work aimed at improving immunogenicity for seasonal use. The development comes as regulators and payers weigh long-term performance for flu vaccines, particularly in year-to-year effectiveness across circulating strains and patient groups.