GSK advances mRNA seasonal flu vaccine to phase III
- Phase II showed higher immune responses versus licensed standard-dose vaccines in adults 18–64 and versus high-dose vaccines in adults ≥65, and was generally well tolerated.
- The candidate targets both haemagglutinin (HA) and neuraminidase (NA), the primary surface antigens of influenza viruses.
- GSK plans to start a phase III efficacy trial in September 2026 and will advance the optimised B-strain HA candidate (FLUm3HA.b-3NA).
- The FDA granted Fast Track designation for the candidate’s targeted age indication in July 2026.
Phase II results
GSK presented phase II data showing its multivalent mRNA seasonal influenza vaccine candidates produced higher immune responses against all influenza strains tested compared with licensed standard-dose vaccines in younger adults and licensed high-dose inactivated vaccines in older adults, and were generally well tolerated through day 181 post-vaccination.
Vaccine design
The programme encodes both haemagglutinin (HA) and neuraminidase (NA) to target the two primary surface antigens involved in binding and spread; GSK says the dual-target approach may improve protection, illness severity and transmission versus HA-only vaccines.
Development plan
Based on the phase II data, GSK will advance the optimised B-strain HA candidate (FLUm3HA.b-3NA) into a phase III efficacy trial scheduled to start in September 2026; this will be the first phase III of an mRNA flu vaccine designed to target both HA and NA.
Trial and regulatory notes
Flu-028 was a randomised, observer-blind phase II trial of 971 adults aged 18 and older assessing immunogenicity and safety of multiple dose levels and formulations. In July 2026, the US FDA granted Fast Track designation for the vaccine candidate’s targeted age indication.
Source: GSK
