GSK Completes Phase 2a Flu Shots Trial in Adults

GSK said its flu shots study of mRNA-based seasonal influenza vaccine candidates is complete, marking a Phase 2a milestone in adults 18 years of age and older. The randomized, observer-blind trial tested two experimental vaccines against existing flu vaccine combinations and was built to measure immune response and safety in healthy adults.

GSK6479720A and GSK6479715A

The study compared Flu mRNA Formulation A, also called GSK6479720A, and Flu mRNA Formulation B, also called GSK6479715A. Each candidate was designed as a single intramuscular dose, and the trial used quadruple masking so participants and observers were assigned to different vaccine groups by chance without knowing which vaccine was given.

Adults 18 Years And Older

GSK’s record lists the study as interventional and Phase 2, with younger and older adult groups running in parallel. That design makes the completed readout more than a simple status update: it is the point at which the company can compare how the two mRNA candidates performed against the existing flu vaccine combinations already in the study.

2026-05-26 Record Update

The trial record shows the status as completed after the last update was submitted on 2026-05-26. The study was first submitted on 2025-08-06, placing the finished Phase 2a update at the center of GSK’s mRNA flu vaccine program as it moves through development in a market where older adults are a core group for seasonal flu shots worldwide.

For readers tracking the program, the immediate next step is not another trial label but the study data itself: whether the two experimental mRNA shots produced immune responses and safety findings strong enough for GSK to keep advancing them.