GSK plc is advancing its investigational mRNA seasonal flu vaccine candidate into Phase III testing after Phase II results demonstrated stronger immune responses compared to standard and high-dose licensed vaccines in both younger and older adults, according to Alliance News and RTTnews reports. The London-based pharmaceuticals company presented the data at the OPTIONS XIII Conference for the Control of Influenza in Washington, DC, noting that the candidate was generally well tolerated.
Phase II Trial Results and Vaccine Design
The Flu-028 Phase II study was a randomised, observer-blind trial assessing the immunogenicity and safety of GSK’s multivalent mRNA flu candidate, which enrolled 971 adults across various age groups, according to RTTnews. Participants aged 18 to 64 as well as those 65 and older were administered varying dose strengths of experimental options—such as the enhanced B-strain variant FLUm3HA.b-3NA, the non-optimised FLUm3HA-3NA, or standard comparators suitable for each age group. Up to day 181, follow-up metrics demonstrated that the refined candidate, FLUm3HA.b-3NA, elicited superior immune activation against both influenza A and B variants while keeping a safe and acceptable profile.
Unlike traditional flu shots that primarily target haemagglutinin (HA), GSK’s messenger RNA vaccine candidate is designed to target both HA and neuraminidase (NA), the two primary surface proteins that allow flu viruses to bind and spread, according to company explanations cited by Alliance News and RTTnews. Growing evidence suggests this dual approach could improve protection, reduce illness severity, and limit transmission. At a standard dose for younger adults and a higher dose for older adults, the candidate showed higher immune responses against all flu types compared with currently licensed vaccines.
Did you know? As noted in findings shared by Sanjay Gurunathan—head of vaccines and infectious diseases research and development at GSK—and covered by Alliance News and RTTnews, seasonal influenza continues to present a significant international health burden, triggering up to one billion infections and claiming as many as 650,000 lives globally every year.
Phase III Trial Timeline and Regulatory Status
The Phase III trial is scheduled to begin in September 2026, marking the first late-stage study of an mRNA flu vaccine targeting both HA and NA, according to RTTnews. This upcoming trial represents a key milestone in GSK’s broader mRNA vaccine program aimed at expanding options for seasonal flu prevention and addressing gaps in current vaccination strategies. In July 2026, the U.S. Food and Drug Administration granted the vaccine Fast Track designation, underscoring the urgent need for improved flu protection, as reported by RTTnews.
Following the Phase II data release, GSK shares rose 0.2% to 1,858.00 pence in London, according to Alliance News reporting. RTTnews noted that the company’s stock closed a prior trading session at $50.25, down 1.12%, before trading slightly lower pre-market.
Pro Tip: Understanding Dual-Targeting Vaccines
While conventional influenza vaccines focus primarily on haemagglutinin mutations, next-generation mRNA candidates incorporating neuraminidase targets aim to disrupt both viral entry and release phases, potentially offering broader cross-strain protection during severe flu seasons.
Frequently Asked Questions
What technology does GSK’s new flu vaccine candidate use?
The vaccine candidate uses messenger RNA technology to target both haemagglutinin (HA) and neuraminidase (NA) molecules, whereas currently licensed vaccines primarily target only HA.
When will the Phase III trials begin?
The Phase III clinical trial is set to begin in September 2026, according to RTTnews.
What were the main findings of the Phase II trial?
According to Alliance News and RTTnews, the candidate showed higher immune responses against all flu types compared with licensed vaccines at standard doses for younger adults and higher doses for older adults, and was generally well tolerated.
Has the vaccine received any regulatory designations?
Yes, the U.S. FDA granted the vaccine Fast Track designation in July 2026, as reported by RTTnews.
What are your thoughts on the development of mRNA-based influenza vaccines? Share your perspective in the comments below, explore our latest pharmaceutical industry reports, or subscribe to our newsletter for weekly updates.
Related reading