GSK is moving its mRNA seasonal influenza vaccine into Phase III after positive Phase II results showed stronger immune responses than licensed flu vaccines in both younger and older adults.

 

The company presented the data at the OPTIONS XIII Conference for the Control of Influenza, saying its vaccine candidate generated higher immune responses against all influenza strains tested compared with licensed standard-dose vaccines in younger adults and high-dose vaccines in older adults. The candidate was also generally well tolerated.1

 

GSK plans to begin a Phase III efficacy trial in September 2026.

 

The trial is set to be the first Phase III study of an mRNA flu vaccine designed to target both haemagglutinin (HA) and neuraminidase (NA) — the two major surface proteins involved in how influenza infects and spreads.

 

Most currently licensed flu vaccines primarily target HA. GSK’s candidate is designed to target NA as well, an approach the company says could potentially improve protection, reduce illness severity and limit transmission.1,3

 

Sanjay Gurunathan, GSK Head of Vaccines and Infectious Diseases Research and Development (R&D), said: “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. This result is a significant advance in our cutting-edge mRNA programme, and we look forward to starting phase III imminently.”

 

The programme received a further regulatory boost in July 2026, when the US Food and Drug Administration granted GSK’s vaccine candidate Fast Track designation for the targeted age indication, underscoring the need for improved influenza protection.

 

The Flu-028 Phase II trial was a randomised, observer-blind study involving 971 adults aged 18 and over. Researchers assessed the immunogenicity and safety of different mRNA-based multivalent seasonal influenza vaccine candidates.

 

Adults aged 18–64 and those aged 65 and over received different dose levels of either FLUm3HA.b-3NA, which encodes an optimised B-strain HA, FLUm3HA-3NA, which encodes non-optimised B/HA, or licensed, age-appropriate comparator vaccines.

 

Immunogenicity and reactogenicity/safety were assessed through day 181 after vaccination.

 

The results showed that GSK’s FLUm3HA.b-3NA candidates generated robust immune responses against both HA and NA from influenza A and B strains in younger and older adults. The vaccines also demonstrated acceptable reactogenicity and safety profiles.1

 

GSK will now take the optimised B-strain HA candidate, FLUm3HA.b-3NA, into a Phase III efficacy trial.

 

The move follows earlier research identifying persistent gaps in influenza vaccination, including the potential importance of NA and the need to strengthen immune responses against B-strain HA.

 

GSK’s investigational mRNA seasonal influenza programme is designed to broaden the immune response by targeting both HA and NA. The programme forms part of the company’s wider respiratory vaccine research and its efforts to develop new approaches to seasonal flu prevention.

 

The candidate is still experimental and is not approved anywhere in the world.