GSK Advances mRNA Flu Vaccine to Phase III
GSK is advancing its mRNA seasonal influenza vaccine candidate FLUm3HA.b-3NA into a Phase III efficacy trial starting in September.
GSK intends to move its mRNA seasonal influenza vaccine candidate to a Phase III efficacy trial starting in September.
The move is based on presented positive Phase II data for its vaccine candidate at the Options XIII Conference for the Control of Influenza, where the candidate showed higher immune responses against all influenza strains compared with licensed standard dose and high dose inactivated flu vaccines in younger and older adults respectively.
The planned Phase III trial will be the first for an mRNA flu vaccine designed to target both haemagglutinin (HA) and neuraminidase (NA), the primary surface antigens that cause the flu virus to bind and spread. While licensed flu vaccines primarily target HA, GSK's candidate is specifically designed to also target NA, and growing evidence suggests this dual-target approach could help improve protection, illness severity and transmission.1
What did the Flu-028 trial show?
Flu-028 is a randomized, observer-blind Phase II trial assessing the immunogenicity and safety of mRNA-based multivalent seasonal flu vaccine candidates in 971 adults 18 years of age and older.2 Adults 18 to 64 and those 65 and older received different dose levels of either FLUm3HA.b-3NA, which encodes an optimized B-strain HA, FLUm3HA-3NA, which encodes a non-optimized B/HA, or licensed age-appropriate comparators, with immunogenicity and reactogenicity and safety data assessed up to day 181 post-vaccination.1
GSK's FLUm3HA.b-3NA vaccine demonstrated robust immune responses to HA and NA from influenza A and B strains in both younger and older adults, along with its reactogenicity and safety profiles across the vaccines being acceptable.2 Based on those results, GSK will advance the optimized B-strain HA candidate, FLUm3HA.b-3NA, into the Phase III efficacy trial.1,2
"Despite the complexity and some of the risks and the challenges in the macro environment, what doesn't change is the fact that vaccines remain the number one most cost-effective and simple intervention to prevent disease. That's just the bottom line," said Sylvia Taylor, EVP of corporate affairs, Head of Novavax Sweden, Novavax in
Why does targeting neuraminidase matter?
Previous studies have highlighted gaps in flu vaccination, including the role of NA and the need to improve B-strain HA immunogenicity. Because licensed vaccines have historically focused on HA alone, GSK's dual-target design represents a departure intended to address protection gaps that current standard and high dose inactivated vaccines have left unresolved.1
"These promising data support the potential to better protect people from flu with a vaccine designed to target both HA and NA. With one billion flu cases worldwide each year and up to 650,000 deaths there is a need for next generation vaccine approaches," said Sanjay Gurunathan, GSK head of vaccines and infectious diseases research and development. "This result is a significant advance in our cutting-edge mRNA program, and we look forward to starting Phase III imminently."
What's next for the program?
Back in July 2026, FDA granted the vaccine candidate Fast Track designation for the targeted age indication, reflecting the urgent need to improve flu protection.1 As of today, GSK's investigational mRNA seasonal flu vaccine program is part of the company's broader respiratory vaccines research and its ongoing work to explore new approaches to seasonal flu prevention.1 It is currently not approved anywhere in the world.
Sources
- GSK to advance mRNA seasonal flu vaccine candidate to phase III following positive phase II data GSK September 1, 2026,
https://www.gsk.com/en-gb/media/press-releases/gsk-to-advance-mrna-seasonal-flu-vaccine-candidate-to-phase-iii-following-positive-phase-ii-data/ - A Study to Find and Confirm the Dose and Assess Safety, Reactogenicity and Immune Response of a Vaccine Against Pandemic H5N1 Influenza Virus in Healthy Younger and Older Adults National Library of Medicine February 5, 2026,
https://clinicaltrials.gov/study/NCT06382311
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