GSK Advances Dual-Target mRNA Flu Vaccine to Phase 3 Trial
- GSK will start a Phase 3 trial of its mRNA seasonal flu vaccine after Phase 2 data (Flu-028, ~971 adults) showed stronger immune responses against every tested flu strain than licensed comparator vaccines, with acceptable tolerability.
- Unlike most approved flu shots, which target only hemagglutinin (HA), GSK's candidate also encodes neuraminidase (NA), the second major surface protein flu uses to spread between cells.
- Growing evidence suggests adding an NA response could improve protection, reduce illness severity, and limit transmission compared with HA-only vaccines.
- The Phase 3 trial will be the first late-stage study of a dual HA/NA mRNA flu vaccine, positioning GSK against Moderna's newly approved single-target mRNA flu shot.
- The FDA granted the candidate Fast Track designation in July 2026, and GSK expects to begin the pivotal trial this month.
GSK's bet: that the stronger immune responses seen in Phase 2 translate into real clinical benefit — fewer infections, milder illness, less transmission — which an HA-only shot like Moderna's already-approved mRNA flu vaccine can't match. This is the first real Phase 3 test of the "NA matters" thesis, not yet proven at scale. It's a platform signal as much as a product one. After lagging Pfizer/Moderna's first-generation, single-antigen mRNA vaccines, a Phase 3 win would show GSK's mRNA engine can handle more complex, multi-antigen constructs. Flu vaccines are a large but seasonal, commoditized, price-pressured market — the real payoff isn't flu revenue itself, it's flu as the proving ground before GSK extends dual/multi-antigen mRNA into RSV, combo respiratory shots, or pandemic-response platforms. If it works, expect the mRNA flu narrative to shift from "mRNA vs. egg-based" to "how many antigens can you stack" — the next competitive axis in a race that's outgrowing its first generation.
GSK catches phase 3 fever after mRNA flu vaccine beats standard shots ↗