GSK’s Dual‑Antigen mRNA Flu Vaccine Enters Phase III Trial

GSK plc has moved its investigational mRNA seasonal influenza vaccine into Phase III trials following Phase II data that demonstrated superior immune responses versus conventional and high‑dose flu vaccines across adult age groups. The findings were reported at the OPTIONS XIII Conference on Influenza Control in Washington, D.C.

Seasonal influenza remains a serious worldwide health issue, accounting for up to one billion infections and roughly 650,000 deaths each year. Existing vaccines focus mainly on haemagglutinin (HA), a surface protein of the virus. GSK’s investigational vaccine, however, is engineered to elicit immune responses against both HA and neuraminidase (NA)—the two key viral antigens implicated in infection, replication and spread. Mounting research suggests that a bivalent HA/NA targeting strategy may enhance protection, lessen disease severity and curb transmission.

The Phase III trial, slated to launch in September 2026, will be the first late‑stage evaluation of an mRNA influenza vaccine that targets both HA and NA antigens. The candidate showed a favorable safety profile in Phase II, which enrolled 971 adults of various ages and generated strong immune responses against influenza A and B strains.

The Flu‑028 Phase II study was a randomized, observer‑blind trial evaluating the immunogenicity and safety of GSK’s multivalent mRNA influenza vaccine candidates. Participants aged 18‑64 and ≥ 65 received varying dose levels of either FLUm3HA.b‑3NA (an optimized B‑strain HA), FLUm3HA‑3NA (a non‑optimized B‑HA), or licensed age‑appropriate comparator vaccines.

Through day 181 of follow‑up, the optimized formulation FLUm3HA.b‑3NA elicited superior immune responses against both influenza A and B viruses while maintaining an acceptable safety and tolerability profile. These results underpin the progression of FLUm3HA.b‑3NA into Phase III efficacy testing.

In July 2026 the U.S. Food and Drug Administration awarded the candidate Fast Track designation, recognizing the urgent need for better influenza protection and the promise of next‑generation vaccine technologies.

The forthcoming Phase III study marks a pivotal milestone in GSK’s expanding mRNA vaccine portfolio, aimed at broadening seasonal flu prevention options and addressing limitations of current vaccination approaches.

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