GSK moves mRNA flu vaccine into late-stage trial after promising mid-stage results

Moderna only just became the first company to win U.S. approval for an mRNA-based flu vaccine. GSK wants to go further. The British drugmaker announced on Tuesday that it will advance its own mRNA seasonal influenza vaccine candidate into a late-stage trial, after mid-stage data showed it produced stronger immune responses than both standard-dose and high-dose flu shots currently on the market, in adults young and old.

What sets GSK's candidate apart is its design. Most flu vaccines target a single surface protein. This one targets two: haemagglutinin and neuraminidase. GSK says that dual approach could improve protection and reduce transmission, though those claims will need late-stage data to hold up. The company says this will be the first phase-three trial of any mRNA flu vaccine built around both proteins.

The trial is set to begin this month.

How does it work?

mRNA vaccines work by instructing the body's own cells to produce a protein that the immune system learns to recognize and fight. In the case of flu, most approved vaccines focus on haemagglutinin, the protein the virus uses to attach to human cells. Neuraminidase is the protein it uses to spread between cells once infection has taken hold. By targeting both, GSK's candidate aims to block the virus at two distinct stages of infection. The mid-stage trial results suggest that combination is generating a measurably stronger immune response than existing options, including high-dose shots that were specifically developed for older adults with weaker immune systems.

Why does it matter?

Influenza kills hundreds of thousands of people globally each year. Vaccine effectiveness for flu has historically been inconsistent, often falling below 50% in years when the circulating strains drift from what manufacturers predicted. A vaccine that targets two surface proteins instead of one could be more resilient to that kind of mismatch. For the GCC region, where large-scale population gatherings, including Hajj and Umrah, create significant seasonal respiratory disease risk, a more effective flu vaccine has direct public health relevance. Saudi Arabia and the UAE have both expanded their immunization programmes in recent years as part of broader health system reforms tied to Vision 2030 and the UAE's national preventive health strategy.

The context

This move is also part of a wider acceleration at GSK. CEO Luke Miels has been pushing the company to speed up drug development as it faces a wave of patent expirations on existing products. As part of that push, GSK plans to start more than 20 late-stage studies before the end of 2026. The mRNA flu vaccine is one of the first to move forward under that plan.

But the broader mRNA flu race is already underway. Moderna's mFlusiva received U.S. approval in August for adults aged 50 and older, marking the first regulatory green light for any mRNA flu vaccine anywhere. GSK is now competing in a space that just opened up, and it is doing so with a more complex scientific bet. Whether that bet pays off will depend on what the phase-three data shows. Still, the early results are difficult to ignore.