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Study of mRNA-based seasonal influenza vaccine to evaluate immune response and safety in adults 18 years 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 focuses on testing new mRNA-based seasonal influenza vaccines in adults aged 18 and older. The study will evaluate different vaccine candidates that target various strains of the influenza virus, including both A and B types. The purpose is to assess how well these vaccines stimulate an immune response and to evaluate their safety.

The study involves several different vaccine formulations that will be given as a single intramuscular injection. Some participants will receive the experimental mRNA vaccines, while others will receive traditional inactivated influenza vaccines for comparison. Each participant will receive one 0.5 milliliter dose of the assigned vaccine.

After vaccination, participants will be monitored for immune response through blood tests and for any side effects for up to 6 months. The study will track both expected injection site reactions and any unexpected health events. Participants will need to record their symptoms in an electronic diary and attend several follow-up visits to the study site for health checks and blood samples.

The research process

The trial runs in 4 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial visit

    The study begins with signing the informed consent document

    A medical examination and evaluation of your health status will be performed

    A urine pregnancy test will be conducted for women of childbearing potential

    Your body mass index (BMI) will be checked to ensure it is between 18 and 33 kg/m²

  2. Step 2

    Vaccination day (Day 1)

    You will receive one intramuscular injection of the study vaccine

    Laboratory tests will be performed before the vaccination

    You will need to remain at the study site for observation after vaccination

  3. Step 3

    Follow-up visits

    Visit on Day 3: Laboratory tests will be performed

    Visit on Day 8: Laboratory tests will be performed

    Visit on Day 29: Laboratory tests and measurement of immune response will be performed

    You will need to record any injection site reactions or symptoms in an electronic diary for 7 days after vaccination

    Any health-related events will be monitored for 28 days after vaccination

  4. Step 4

    Extended monitoring period

    Your health status will be monitored for a total of 6 months after vaccination

    Any significant medical events during this period should be reported

    The study is expected to continue until July 2026

Who can join the trial?

10 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 either healthy or have stable medical conditions. A stable condition means:
    • No major changes in treatment in the last 3 months
    • No hospital stays for worsening condition in the last 3 months
    • For women who can become pregnant:
      • Must use effective birth control for at least 4 weeks before the study
      • Must have a negative pregnancy test within 24 hours before starting
      • Must continue birth control for at least 8 weeks after 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)
      • Women who cannot become pregnant (e.g., post-menopausal) may also participate

Who cannot join the trial?

13 criteria

  • History of severe allergic reactions to any vaccine components or life-threatening reactions to previous flu vaccines
  • Current participation in another clinical trial or use of any investigational drug within 30 days before the study
  • Received any vaccine within 30 days before the study vaccine
  • Active acute illness or fever (temperature ≥38.0°C/100.4°F) at the time of vaccination
  • Known or suspected problems with the immune system (immunodeficiency)
  • Currently receiving medications that suppress the immune system (immunosuppressive therapy)
  • History of Guillain-Barré syndrome (a rare disorder where the body's immune system attacks the nerves)
  • Bleeding disorders or current use of blood-thinning medications
  • Pregnant women or those planning to become pregnant during the study period
  • Breastfeeding mothers
  • Any chronic medical condition that, in the opinion of the study doctor, makes participation unsafe
  • History of severe allergic reactions (anaphylaxis) to any substance
  • Receipt of blood products or immunoglobulins (antibody treatments) within the past 3 months
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Investigated drugs

Based on the provided trial information, this appears to be a study of: mRNA-based multivalent seasonal influenza vaccine - This is an investigational vaccine that uses messenger RNA (mRNA) technology to help protect against multiple strains of seasonal influenza (flu). Unlike traditional flu vaccines that use inactivated or weakened viruses, this vaccine uses genetic material (mRNA) to teach the body's cells how to make proteins that trigger an immune response against flu viruses. The "multivalent" aspect means it targets several different flu strains at once. Note: Since the trial data doesn't specify other medications or therapies being tested, only the mRNA flu vaccine candidate can be listed. While there may be a placebo involved as this is a randomized study, as per instructions, placebo products are not included in this description.

What is already known about the treatment

mRNA Influenza Vaccine - An innovative vaccine administered through intramuscular injection that uses messenger RNA technology to protect against seasonal influenza virus strains. This investigational vaccine is currently undergoing Phase 2a clinical trials to evaluate its safety and effectiveness in adults aged 18 and older. The vaccine works by delivering genetic instructions to cells to produce specific viral proteins, which then trigger an immune response, teaching the body to recognize and fight actual influenza viruses. It represents a new approach in vaccine development, belonging to the class of nucleic acid-based vaccines, and aims to provide more effective protection against multiple influenza strains compared to traditional flu vaccines.

Investigated diseases

Human Influenza - A respiratory infection caused by influenza viruses that affects the nose, throat, and sometimes lungs. The illness typically begins suddenly with symptoms such as fever, muscle aches, headache, fatigue, cough, and runny nose. It spreads easily from person to person through respiratory droplets when infected people cough, sneeze, or talk. The virus typically causes seasonal epidemics during winter months. Most people recover within a few days to two weeks, but some may develop complications. The virus can change slightly from year to year through a process called antigenic drift.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IITrial ID2025-522599-97-00Protocol code300336Estimated enrolment960 patientsSponsorGlaxoSmithKline Biologicals

sourced from the EU Clinical Trials Register and site verification

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