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Study of mRNA-based seasonal influenza vaccine combinations compared to standard influenza vaccines in adults aged 18 and older

Verified siteRegistered drugNo placebo
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What is this trial about?

A plain-language summary of the goals, design and what participants do

This clinical trial aims to evaluate a new mRNA-based seasonal influenza vaccine in adults. The study focuses on testing different versions of an experimental vaccine against influenza, commonly known as the flu. The vaccines will be given as injections into the muscle.

The study will test several different formulations of the vaccine, including versions containing various influenza virus strains. Some participants will receive the experimental mRNA vaccine candidates, while others will receive currently available flu vaccines for comparison. The study will monitor how well the immune system responds to the vaccines and track their safety.

Participants will receive a single dose of 0.5 milliliters of vaccine and will be monitored for 6 months afterward. During this time, researchers will check for immune responses through blood tests and record any side effects that occur. The study will look at both expected injection site reactions and any unexpected health events that might happen after vaccination.

The research process

The trial runs in 5 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial visit and vaccination

    On Day 1, you will receive a single intramuscular injection of the study flu vaccine.

    Before vaccination, a blood sample will be taken and laboratory tests will be performed.

    You will need to stay at the study site for observation after receiving the vaccine.

  2. Step 2

    Early follow-up visits

    You will need to visit the study site on Day 3 and Day 8 for blood tests and safety monitoring.

    During the first 7 days after vaccination, you will need to record any injection site reactions (such as pain or redness) or general symptoms in an electronic diary.

  3. Step 3

    Main follow-up visit

    On Day 29, you will need to visit the study site for blood tests to measure your immune response to the vaccine.

    The study team will review any health changes you experienced since the vaccination.

  4. Step 4

    Extended monitoring period

    For 6 months after vaccination, any significant medical events will need to be reported.

    The study will monitor for any serious health events or specific medical conditions of interest during this period.

  5. Step 5

    Final assessment

    The study will conclude 6 months after your vaccination.

    This will include a final review of your health status and any medical events that occurred during the study period.

Who can join the trial?

9 criteria

  • Must be able to follow study requirements independently or with caregiver help, including completing electronic diaries and attending study visits
  • Must provide written consent (on paper or digitally) before any study procedures begin
  • Must be at least 18 years old at screening
  • Must be healthy or have stable medical conditions that haven't required major treatment changes or hospital stays in the past 3 months
  • For women who cannot become pregnant: can participate without additional requirements
  • For women who can become pregnant must:
    • Use effective birth control for at least 4 weeks before the study
    • Have a negative pregnancy test within 24 hours before starting
    • Continue using birth control for 8 weeks after receiving study treatment
    • Must have a body mass index (BMI) between 18 and 33 kg/m² (BMI is a measure of body fat based on height and weight)

Who cannot join the trial?

12 criteria

  • History of severe allergic reactions to any vaccine component or life-threatening allergies
  • Previous vaccination against influenza within the last 6 months
  • Current participation in another clinical trial or within 30 days before this study
  • Pregnancy or breastfeeding
  • Any immunodeficiency condition (weakened immune system due to disease or medication)
  • Acute illness or fever (temperature above 38°C/100.4°F) at the time of vaccination
  • Receipt of immunoglobulins (antibody treatments) or blood products within 3 months before the study
  • History of Guillain-Barré syndrome (a rare disorder where the immune system attacks the nerves)
  • Chronic medical conditions that are not well controlled
  • Use of medications that affect the immune system
  • History of severe reactions to previous influenza vaccines
  • Any condition that, in the opinion of the investigator, might interfere with the study evaluations
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Investigated drugs

  • Investigational mRNA influenza vaccine (GSKVX000000034794, GSKVX000000034798, GSKVX000000048110, GSKVX000000048111, GSKVX000000070248, GSKVX000000070250)

    This is a new vaccine that uses messenger RNA technology to teach the body’s immune system to recognize several flu viruses at once. The vaccine is given as a small injection into the muscle. It is being tested to see if it can safely produce a strong antibody response against the seasonal flu strains included in the study.

  • Alpharix trivalent influenza vaccine

    This is a traditional flu shot that contains three inactivated (killed) flu viruses: one type B strain from Austria, one type A H1N1 strain from Victoria, and one type A H3N2 strain from Thailand. The viruses are fragmented and mixed in a liquid that is injected into the muscle. The vaccine is used as a comparison to see how the new mRNA vaccine performs.

  • Inactivated split‑virus influenza vaccine

    This comparator vaccine also contains three flu viruses (A H1N1, A H3N2, and B) that have been chemically inactivated and then split into smaller pieces. These pieces are mixed in a suspension for injection into the muscle. It provides protection by exposing the immune system to the virus fragments without causing disease.

  • Recombinant haemagglutinin influenza vaccine

    This vaccine is made from laboratory‑produced haemagglutinin proteins (the part of the flu virus that triggers immunity) for the three strains: A H1N1, A H3N2, and B Victoria lineage. The recombinant proteins are dissolved in a solution for injection into the muscle. It serves as another reference vaccine to compare the immune response and safety of the investigational mRNA product.

What is already known about the treatment

mRNA Influenza Vaccine - An investigational vaccine administered via intramuscular injection that uses messenger RNA technology to protect against seasonal influenza virus strains. This novel vaccine approach, currently in Phase 2a clinical trials, works by delivering genetic instructions to cells to produce specific viral proteins that trigger an immune response against influenza. The vaccine belongs to the class of nucleic acid-based immunizations and represents a new direction in influenza prevention, differing from traditional egg-based flu vaccines. The primary goal is to generate protective antibodies against multiple influenza strains while maintaining a favorable safety profile, potentially offering broader protection than conventional seasonal flu vaccines.

Investigated diseases

Influenza - A highly contagious viral respiratory infection that affects the nose, throat, and sometimes the lungs. The virus spreads through tiny droplets when infected people cough, sneeze, or talk. Symptoms typically appear suddenly and include fever, chills, muscle aches, fatigue, headache, dry cough, and runny nose. The illness usually develops within 1-4 days after exposure to the virus. The intensity of symptoms can vary from mild to severe, with most people recovering within a week to ten days.
Trial detailsLast updated 22 Oct 2026
Age18+ yearsPhasePhase IITrial ID2025-522278-35-00Protocol code300356Estimated enrolment770 patientsSponsorGlaxoSmithKline Biologicals

sourced from the EU Clinical Trials Register and site verification

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