GSK presented positive phase 2 data for its mRNA seasonal influenza (flu) vaccine candidate at the OPTIONS XIII Conference for the Control of Influenza.

GSK’s vaccine candidate showed higher immune responses against all influenza strains tested compared to licensed standard dose and high dose inactivated flu vaccines in younger and older adults respectively, and was generally well tolerated.

Based on these results, GSK intends to start a phase 3 efficacy trial in September 2026.

This will be the first phase 3 trial of 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 vaccine candidate is specifically designed to also target NA. Growing evidence suggests this could help improve protection, illness severity and transmission.

Sanjay Gurunathan, Head of Vaccines and Infectious Diseases Research and Development (R&D), GSK, said, “These promising data support the potential to better protect people from flu with a vaccine designed to target both HA and NA. With 1 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 3 imminently.”

In July 2026, the US Food and Drug Administration (FDA) granted the vaccine candidate Fast Track Designation (FTD) for the targeted age indication, reflecting the urgent need to improve flu protection.

Flu-028 is a randomised, observer-blind phase 2 trial assessing the immunogenicity and safety of mRNA-based multivalent seasonal flu vaccine candidates in 971 adults 18 years of age and older. Adults 18 to 64 and ≥65 years of age received different dose levels of either FLUm3HA.b-3NA (encoding an optimised B-strain HA), FLUm3HA-3NA (encoding non-optimised B/HA) or licensed age-appropriate comparators. Immunogenicity and reactogenicity/safety data up to day 181 post-vaccination were assessed.

Previous studies highlighted the gaps in flu vaccination, including the role of NA and the need to improve B-strain HA immunogenicity. In the Flu-028 phase 2 trial, GSK’s FLUm3HA.b-3NA flu vaccines demonstrated robust immune responses to HA and NA from influenza A and B strains in younger and older adults. Reactogenicity and safety profiles of the vaccines were acceptable.

Based on the results, GSK will further investigate the optimised B-strain HA (FLUm3HA.b-3NA) candidate in a phase 3 efficacy trial.

The company’s investigational mRNA seasonal flu vaccine program is designed to target HA NA. It is part of GSK's respiratory vaccines research and ongoing work to explore new approaches to seasonal flu prevention.

The mRNA seasonal flu vaccine candidate is not approved anywhere in the world.