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Immunogenicity and safety of intradermal zoonotic influenza vaccine (H5N8) compared with intramuscular administration in adults 40–80 years with avian influenza

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What is this trial about?

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

The study focuses on Avian Influenza, a type of flu that can spread from birds to humans. Participants will receive a new zoonotic influenza vaccine (H5N8), which is designed to protect against this virus. The vaccine is given in two different ways: directly into the skin (intradermal) or into the muscle (intramuscular). A harmless solution called placebo is also used for comparison. The purpose of the study is to show that the immune response from the skin injection is not worse than that from the muscle injection.

Adults aged 40 to 80 will receive two doses of the assigned injection, spaced about one month apart. After each dose, participants will be observed for any side effects, such as soreness at the injection site or general feelings of illness, and will be followed for several months to record any health events. The study collects information on how well the vaccine works and whether it is safe, using simple blood tests and health questionnaires.

The research process

The trial runs in 13 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Enrollment and Baseline Assessments

    After signing the informed consent form, you will undergo basic health checks, including a physical exam and blood tests, to confirm eligibility for the study.

    Your medical history will be recorded, and you will receive information about the study procedures and what to expect.

  2. Step 2

    First Injection (Day 1)

    On the first day, you will receive a single injection of either the influenza vaccine (containing the H5N8 strain) or a placebo (sodium chloride 0.9%).

    The injection is given either into the skin (intradermal) or into the muscle (intramuscular), depending on the random assignment.

    The exact amount of vaccine is not disclosed, but the dose is administered once at this visit.

  3. Step 3

    Immediate Post‑Injection Observation

    You will be observed at the clinic for about 30 minutes after the injection to monitor any immediate reactions.

    If any symptoms such as redness, swelling, or faintness occur, the study staff will assess you before you leave.

  4. Step 4

    Daily Diary for the First 7 Days

    For the next seven days, you will record any side effects at the injection site (such as pain, redness, or swelling) and any general symptoms (such as fever, headache, or fatigue) in a diary provided by the study.

    These records help the study evaluate solicited adverse events.

  5. Step 5

    Follow‑Up Visit (Day 7)

    You will return to the clinic one week after the first injection for a brief check‑up.

    The study team will review your diary, examine the injection site, and ask about any other symptoms that may have appeared.

  6. Step 6

    Extended Monitoring (Days 8–28)

    During the three weeks after the first injection, you should continue to note any health changes, especially those that were not expected (called unsolicited adverse events).

    If you experience any serious problems, you are instructed to contact the study staff immediately.

  7. Step 7

    Second Injection (Day 57)

    Approximately eight weeks after the first dose, you will receive a second injection of the same product (vaccine or placebo) using the same route as before.

    This second dose follows the same procedure as the first dose.

  8. Step 8

    Immediate Post‑Second Injection Observation

    Again, you will be observed for about 30 minutes at the clinic to ensure there are no immediate reactions.

  9. Step 9

    Daily Diary for the Second 7 Days

    For the seven days following the second injection, you will record any injection‑site or systemic symptoms in the diary, just as after the first dose.

  10. Step 10

    Second Follow‑Up Visit (Day 64)

    One week after the second injection, you will attend a clinic visit where the study staff will review your diary, examine the injection site, and discuss any side effects.

  11. Step 11

    Extended Monitoring After Second Dose (Days 65–85)

    During the three weeks after the second injection, you continue to note any unexpected health events. These are classified as unsolicited adverse events.

  12. Step 12

    Final Assessment (Day 181)

    Six months after the first injection (Day 181), you will attend a final study visit.

    Blood samples will be taken to measure the immune response to the vaccine, and the study team will ask about any serious health problems that occurred during the six‑month period.

  13. Step 13

    Study Completion

    After the final assessment, the study concludes for you. You will receive a summary of the overall study results once they are publicly available.

Who can join the trial?

7 criteria

  • Be able to follow the study requirements, such as completing a diary and attending all planned visits.
  • Give written informed consent, meaning you understand the study information and agree to take part.
  • Be between 40 and 80 years old at the time the first vaccine dose is given.
  • Be considered medically stable by the doctor, meaning any long‑term health problems (for example, high blood pressure or heart disease) are well‑controlled and are not expected to affect the immune response.
  • If you are a female who cannot become pregnant (non‑childbearing potential), you may join the study. This includes women who have had a hysterectomy, removal of both ovaries, removal of both fallopian tubes, or who are post‑menopausal (no periods for 12 months without another medical cause).
  • If you are a female who could become pregnant (childbearing potential), you may join the study only if you:
    • have used reliable birth control for at least one month before the first vaccine dose and agree to keep using it until the study ends, and
    • are not pregnant on the day of the first vaccine dose, confirmed by a medical history interview and a pregnancy test.

Who cannot join the trial?

24 criteria

  • Allergic reaction or hypersensitivity to any ingredient in the vaccine, such as egg or chicken protein, ovalbumin, formaldehyde, hydrocortisone, kanamycin, neomycin sulphate, or CTAB.
  • Body mass index (BMI) less than 18 or greater than 30 kg/m² (a measure of body weight relative to height).
  • A tattoo or skin sore on the upper arm or forearm where the shot would be given, making it impossible to check for local side effects.
  • Any known or suspected condition that weakens the immune system, such as current cancer, HIV infection, or medicines that suppress immunity (e.g., chemotherapy, organ‑transplant drugs, or treatments for autoimmune diseases).
  • Being a study staff member or an immediate family or household member of someone on the study team.
  • Repeated or uncontrolled neurological problems or seizures (controlled neurological conditions may be allowed after assessment).
  • A serious or unstable long‑term illness.
  • History of dementia or any condition that seriously affects thinking or memory.
  • A major underlying illness that the doctor believes would stop you from finishing the study.
  • Any medical problem that would make an intramuscular (into the muscle) or intradermal (into the skin) injection unsafe.
  • Any serious adverse event (SAE) that was linked to a previous flu‑vaccine dose.
  • Having received a H5N1 vaccine or any other vaccine that contains the H5 virus strain before.
  • Any other health condition that the doctor feels could increase the risk of participating.
  • Testing positive for hepatitis B surface antigen (HBsAg), hepatitis C antibodies, or HIV.
  • Past or current autoimmune disease (where the immune system attacks the body’s own tissues).
  • Use of any experimental or non‑approved drug, vaccine, or medical device within 28 days before the first shot and until the study ends.
  • Planning to receive a live attenuated vaccine (a vaccine made from weakened live virus) from 28 days before the first shot until 28 days after the second shot.
  • Long‑term use (more than 14 consecutive days) of immune‑modifying medicines, or planned use of long‑acting immune‑modifying treatments, up to the end of the study. This includes:
    • Prednisone (or equivalent) 20 mg per day or higher for up to 3 months before the first shot (inhaled or skin steroids are allowed).
    • Immunoglobulins or blood products.
    • Long‑acting drugs such as TNF‑inhibitors, monoclonal antibodies, or cancer‑type medicines used within 6 months before the first shot.
    • Being enrolled in another clinical study that involves an experimental or non‑experimental drug or device at any time during this study.
    • Being pregnant or breastfeeding.
    • Being a female who plans to become pregnant or intends to stop using birth‑control methods.
    • History of chronic alcohol use or drug abuse that might prevent accurate safety reporting or following study procedures.
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Investigated drugs

Zoonotic influenza vaccine (H5N8) is a vaccine made from a killed (inactivated) version of the H5N8 bird flu virus. It contains surface proteins from the virus that help the immune system recognize and fight the real virus if a person is later exposed. The vaccine also includes an adjuvant, which is a substance that boosts the body’s immune response, making the vaccine work better. In this trial the vaccine is given either under the skin (intradermally) or into the muscle (intramuscularly) to see which method produces a strong immune response with acceptable safety. The goal is to show that the skin‑injected version works at least as well as the muscle‑injected version in adults aged 40 to 80 years.

What is already known about the treatment

Zoonotic Influenza Vaccine Seqirus - This vaccine is supplied as a clear liquid in a pre‑filled syringe and is given by injection, either into the muscle or the skin, depending on the study protocol. It is an inactivated (killed) influenza vaccine that is currently being studied in clinical trials and has limited market approval in some countries. The vaccine is intended to protect people from avian influenza caused by the H5N8 virus strain. It works by exposing the immune system to the virus’s surface proteins, which triggers the body to make antibodies, and it is classified as a viral vaccine (purified antigen).

Investigated diseases

Avian Influenza - A viral infection caused by influenza A viruses that primarily affect birds. The virus enters the respiratory tract and replicates in the lining of the airways. Infected individuals may develop fever, cough, sore throat, and muscle aches as the infection spreads. The disease can progress to involve the lungs and other organs, leading to increased respiratory symptoms. Symptoms usually appear a few days after exposure and may last for several weeks.
Trial detailsLast updated 31 Oct 2026
Age18+ yearsPhasePhase ITrial ID2026-525756-28-00Estimated enrolment60 patientsSponsorUniversity Of Antwerp

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