GSK has reported positive Phase II results for its mRNA seasonal influenza vaccine candidate, with the company planning to begin a Phase III efficacy trial in September 2026.
The data were presented at the OPTIONS XIII Conference for the Control of Influenza. GSK said its vaccine candidate produced stronger immune responses against all influenza strains tested when compared with currently licensed flu vaccines. The candidate was generally well tolerated in both younger and older adults.
The planned Phase III study will be the first late-stage trial of an mRNA flu vaccine designed to target both haemagglutinin (HA) and neuraminidase (NA), two key surface proteins of the influenza virus.
Most existing seasonal flu vaccines mainly target HA. GSK’s candidate is designed to target both HA and NA, with the company believing that adding NA could potentially improve protection against influenza, reduce the severity of illness and help limit virus transmission.
Sanjay Gurunathan, GSK’s Head of Vaccines and Infectious Diseases Research and Development, said the Phase II findings support the potential of a vaccine that targets both major influenza surface antigens.
The company highlighted the continued global need for improved influenza vaccines. Influenza causes around one billion cases worldwide each year and can lead to hundreds of thousands of deaths, according to GSK.
The latest results mark an important step forward for GSK’s mRNA vaccine program as the company prepares to move into Phase III development.
In July 2026, the US Food and Drug Administration (FDA) granted Fast Track designation to GSK’s mRNA flu vaccine candidate for its targeted age indication. The designation is intended to support the development and review of treatments and vaccines addressing serious conditions where there is an unmet medical need.
If the Phase III trial confirms the Phase II findings, GSK’s mRNA flu vaccine could represent a new approach to seasonal influenza vaccination by targeting both HA and NA.