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Study of mRNA-based seasonal influenza vaccine to evaluate immune response and safety in adults 18 years and older

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What is this study about?

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.

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 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 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 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 Study?

  • 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 Study?

  • 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

Where you can join this trial?

Verified and Recommended Sites

No sites found in this category

Verified Sites

No sites found in this category

Other Sites

Site Name City Country Status
Universitair Ziekenhuis Gent Gent Belgium
Uhunngoxhb Ot Aemmasu Edegem Belgium

Want to learn more about this study or check if you can participate? Contact us.

Trial status

Country Status Recruitment Start
Belgium Belgium
Not recruiting
10.10.2025

Trial locations

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.

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 ID:
2025-522599-97-00
Protocol code:
300336
NCT ID:
NCT07204964
Trial Phase:
Therapeutic exploratory (Phase II)

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