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Influenza Vaccines / Immunogenicity, Vaccine / Antibodies, Viral · Journal article
Human Vaccines & Immunotherapeutics · June 11, 2026
Encouraging direction, but not yet definitive.
This phase 1/2 trial demonstrates that AS03-adjuvanted H5N8 vaccine induces immune responses meeting FDA criteria for influenza vaccines with an acceptable safety profile in US adults aged 18 years and older. The antigen-sparing potential of the adjuvant was demonstrated, with AS03 A formulation showing superior immunogenicity compared to AS03 B across multiple measures. However, the trial does not include efficacy data, clinical outcomes, or head-to-head comparison with other pandemic preparedness vaccine candidates.
Phase 1/2, observer-blinded, age-stratified, randomized controlled trial. Healthy US adults aged ≥18 years, stratified by age (18–64 years and ≥65 years).. Intervention: AS03-adjuvanted H5N8 influenza vaccine (A/Astrakhan/3212/2020-like) at 3.75 µg or 7.50 µg hemagglutinin antigen with AS03 A or AS03 B adjuvant, two doses 21 days apart.. Compared with: AS03 A versus AS03 B formulations (no non-adjuvanted or standard vaccine control described).. n = 518. United States.
518 of 520 enrolled participants were vaccinated and included in the analysis. FDA criteria for seroprotection, seropositivity, and seroconversion were met on day 43 across vaccine formulations. HI SPRs, seropositivity rates, SCRs, GMTs, and GMFR were higher in AS03 A versus AS03 B groups.
Safety was acceptable, with no increase in adverse events post-dose 2; reactogenicity appeared more common in younger adults.
This trial supports the immunogenicity profile and safety of the 3.75 µg AS03 A formulation licensed in the US for pandemic preparedness. Clinicians should note that immunogenicity data does not yet translate to efficacy or clinical protection; further evaluation in outbreak or challenge settings would be needed to establish clinical benefit, particularly in older adults who showed lower immune responses.
Phase 1/2 trial demonstrating that AS03-adjuvanted H5N8 vaccine met FDA immunogenicity criteria with acceptable safety in adults, but lacks efficacy data and comparative effectiveness evidence needed for practice-changing claims.
As stated by the source record.
Quoted from the source exactly as published.
This trial supports the immunogenicity profile and safety of the 3.75 µg AS03 A formulation licensed in the US for pandemic preparedness. Clinicians should note that immunogenicity data does not yet translate to efficacy or clinical protection; further evaluation in outbreak or challenge settings would be needed to establish clinical benefit, particularly in older adults who showed lower immune responses.
Graded across the dimensions that decide whether you should act, each from what the source actually supports. There is no single score, and where a dimension was not assessed it says so.
Influenza pandemics arise from novel influenza A viruses. Recent emergence of a new clade (2.3.4.4.b) of the highly pathogenic H5N1 in animals and humans highlighted its pandemic potential. We evaluated the immunogenicity and safety of GSK's AS03-adjuvanted H5N8 vaccine in adults. In this phase 1/2, observer-blinded, age-stratified, randomized trial, healthy US adults (age, ≥18 y) received two intramuscular doses of hemagglutinin antigen (3.75 or 7.50 μg) with AS03A or AS03B, administered 21 d apart. Immunogenicity - seroprotection rates (SPRs), seropositivity, geometric mean titers (GMTs), geometric mean fold rise (GMFR), and seroconversion rates (SCRs) - was evaluated on day 43 using hemagglutination inhibition (HI) and microneutralization (MN) assays. Safety was monitored throughout the study. Of 520 enrolled participants, 518 were vaccinated. On day 43, the US Food and Drug Administration's (FDA) Center for Biologics Evaluation and Research criteria for influenza vaccines were met. HI SPRs, seropositivity rates, SCRs, GMTs, and GMFR appeared to be higher in the AS03A vs AS03B group. Immune responses were generally higher in younger (aged 18-64 y) vs older (aged ≥65 y) adults. Immune responses were also detected in MN assays, with a correlation between HI and MN responses on day 43 across age groups and vaccine formulations. Safety was acceptable, with no increase in adverse events post-dose 2. Reactogenicity appeared more common in younger adults. The antigen-sparing potential of AS03 was demonstrated, with an acceptable safety profile. The benefit/risk profile was favorable for all formulations tested, including 3.75 µg AS03A (licensed in the US).ClinicalTrials.gov registration: NCT05975840.
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