GSK is planning to initiate a Phase III efficacy trial of its mRNA-based seasonal influenza (flu) vaccine candidate in September 2026, following positive Phase II results.
The company presented positive Phase II data for its mRNA seasonal flu vaccine candidate at the OPTIONS XIII Conference for the Control of Influenza.
The vaccine candidate demonstrated higher immune responses against all influenza strains tested compared with licensed standard-dose and high-dose inactivated flu vaccines in younger and older adults, respectively. The candidate was also generally well tolerated.
According to GSK, this will be the first phase III 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.
Licensed flu vaccines primarily target HA, but growing evidence suggests targeting both antigens could help improve protection, illness severity and transmission.
Sanjay Gurunathan, GSK Head of Vaccines and Infectious Diseases Research and Development (R&D), said, “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.”
In July 2026, the US Food and Drug Administration (FDA) granted Fast Track designation to the vaccine candidate for its targeted age indication, reflecting the need for improved influenza protection.
About the Flu-028 Phase II Trial
Flu-028 is a randomised, observer-blind Phase II trial evaluating the immunogenicity and safety of mRNA-based multivalent seasonal influenza vaccine candidates in 971 adults aged 18 years and older.
Adults aged 18–64 years and those aged 65 years and older received different dose levels of either FLUm3HA.b-3NA, which encodes an optimised B-strain HA, or FLUm3HA-3NA, which encodes a non-optimised B-strain HA, or licensed age-appropriate comparator vaccines. Immunogenicity, reactogenicity and safety data were assessed through Day 181 following vaccination.
Previous studies have highlighted gaps in influenza vaccination, including the potential role of NA and the need to improve immunogenicity against B-strain HA.
In the Flu-028 Phase II trial, GSK’s FLUm3HA.b-3NA vaccines demonstrated robust immune responses against HA and NA from influenza A and B strains in both younger and older adults. The reactogenicity and safety profiles were also acceptable.
Based on these results, GSK plans to further investigate the optimised B-strain HA candidate, FLUm3HA.b-3NA, in a Phase III efficacy trial.
Seasonal influenza is estimated to cause around one billion cases worldwide each year, including up to five million cases of severe illness and as many as 650,000 respiratory deaths. People at increased risk include older adults, pregnant women and those with underlying health conditions. While vaccination remains the cornerstone of influenza prevention, the disease continues to impose a significant global burden, highlighting the need for ongoing research into next-generation approaches that could improve protection.
