A next-generation influenza vaccine candidate targeting both haemagglutinin (HA) and neuraminidase (NA) is moving into late-stage clinical development, following encouraging Phase II results from GSK.
GSK has announced positive Phase II results for its investigational mRNA seasonal influenza vaccine candidate, with the company planning to initiate a Phase III efficacy trial in September 2026.
The findings add to growing interest in mRNA technology as a platform for developing next-generation influenza vaccines and, in particular, in approaches that target multiple viral antigens.
Beyond haemagglutinin: targeting two key influenza proteins
Most currently licensed influenza vaccines primarily target haemagglutinin (HA), a surface protein that plays a key role in enabling influenza viruses to attach to and enter host cells.
GSK’s investigational vaccine takes a broader approach by targeting both HA and neuraminidase (NA). NA is another major surface protein involved in the release and spread of newly formed virus particles.
Growing evidence suggests that incorporating NA into influenza vaccine strategies could potentially contribute to broader protection and may influence disease severity and viral transmission. GSK is therefore exploring whether combining immune responses against both antigens can address some of the limitations of current influenza vaccines.
Encouraging Phase II immunogenicity data
The Flu-028 Phase II trial included 971 adults aged 18 years and older. Participants in the 18–64 and ≥65 age groups received different dose levels of investigational mRNA vaccine candidates or licensed, age-appropriate influenza vaccines.
The optimised candidate, FLUm3HA.b-3NA, generated robust immune responses against HA and NA from influenza A and B strains. In the study, the mRNA vaccine candidates demonstrated higher immune responses against the influenza strains tested compared with standard-dose influenza vaccines in younger adults and high-dose vaccines in older adults.
The vaccine candidates were generally well tolerated, with acceptable reactogenicity and safety profiles.
Based on these results, GSK has selected the optimised FLUm3HA.b-3NA candidate for further clinical development.
Phase III trial planned for September 2026
The planned Phase III study will move the programme beyond immunogenicity and safety assessment towards evaluating clinical efficacy. This will be an important step in determining whether the immune responses observed in Phase II translate into meaningful protection against influenza infection and illness.
The trial will also represent a notable milestone for mRNA influenza vaccine development: it is expected to be the first Phase III trial of an mRNA influenza vaccine specifically designed to target both HA and NA.
In July 2026, the US Food and Drug Administration (FDA) granted the candidate Fast Track designation for the targeted age indication, reflecting the potential need for improved approaches to influenza prevention.
Why this matters for influenza prevention
Seasonal influenza continues to represent a substantial global health burden, with around one billion cases estimated worldwide each year and up to five million cases of severe illness. Older adults, pregnant women and people with underlying health conditions are among those at increased risk of complications.
While annual vaccination remains the cornerstone of influenza prevention, the continued burden of disease highlights the need for improved vaccine strategies.
mRNA technology could offer greater flexibility in vaccine design, while targeting both HA and NA represents a potential shift towards a broader antigenic approach. Whether this translates into improved clinical protection remains to be demonstrated in Phase III.
GSK’s candidate is currently investigational and is not approved for use anywhere in the world.
The upcoming Phase III programme will therefore provide important evidence on whether combining mRNA technology with dual HA/NA targeting can contribute to the next generation of seasonal influenza vaccines.
Source: GSK, September 2026.
