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Phase 2b Study of VXB-221 and VXB-213 Protein Vaccine for Prevention of Respiratory Syncytial Virus and Human Metapneumovirus Infections in Adults ≥60 Years

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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 infections caused by Respiratory Syncytial Virus and Human Metapneumovirus, viruses that can lead to serious lung problems in older adults. The vaccine being tested is a bivalent protein vaccine called RSV+HMPV protein vaccine (618), which contains two active components named VXB-221 and VXB-213. It is given as an injection into the muscle.

The purpose is to determine whether the vaccine can prevent the first episode of lower respiratory tract disease (LRTD) caused by these viruses within a year. Participants aged 60 and older will be randomly assigned to receive either the vaccine or a saline solution (placebo), and neither the participants nor the study staff will know which was given. Over approximately 12 months, participants will have regular check‑ups to record any respiratory illnesses, reactions at the injection site, and other health events.

Safety monitoring includes looking for any unwanted effects, especially serious adverse events (SAEs) and adverse events of special interest (AESI). Some participants may provide blood samples so the study can measure how well the immune system responds to the vaccine.

The research process

The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial visit and vaccination

    You arrive at the study site after having agreed to take part in the trial. a healthcare professional will confirm that you meet all study requirements.

    You will receive a single dose of either the rsv+hmpv protein vaccine (the test product) or a 0.9% nacl diluent (the placebo). the injection is given intramuscularly in the upper arm.

    The volume of the injection is the amount specified by the study protocol and is administered once at this visit.

  2. Step 2

    Post‑injection observation

    After the injection you will remain at the clinic for about thirty minutes while staff watch for any immediate reactions such as redness, swelling, fever, or feeling unwell.

    If any reaction occurs, staff will provide appropriate care and record the event.

  3. Step 3

    Symptom diary period

    For the next seven days you will keep a written diary to note any symptoms, side effects, or changes in how you feel. this includes local reactions at the injection site (such as pain or swelling) and systemic reactions (such as fever, headache, or fatigue).

    The diary helps the study team evaluate the safety of the vaccine or placebo.

  4. Step 4

    First follow‑up visit (approximately 1 month)

    You will return to the study site about one month after the injection. during this visit staff will ask about any health events that occurred, review your diary, and may collect a small blood sample to measure immune response.

    The visit also includes a brief physical check to ensure you are feeling well.

  5. Step 5

    Subsequent follow‑up visits (3, 6, and 12 months)

    Additional visits are scheduled at roughly three months, six months, and twelve months after the injection. each visit follows the same pattern: discussion of any new health problems, review of any side effects, and collection of a blood sample to assess long‑term immunity.

    These visits continue for a total of twelve months, which is the period used to evaluate whether the vaccine prevents respiratory infections.

  6. Step 6

    Final assessment and study completion

    At the twelve‑month visit the study team will perform a final health assessment, review all collected data, and close your participation in the trial.

    No further study‑specific medication or injections are given after this point.

Who can join the trial?

2 criteria

  • You must be at least 60 years old on the day you join the study.
  • You must be considered eligible by the doctor after a medical evaluation that includes reviewing your medical history (information about past illnesses and health), doing a physical examination (the doctor checks your body), and using the doctor's clinical judgment (professional decision based on the information).

Who cannot join the trial?

5 criteria

  • Having a weakened immune system (known or suspected), having taken medicines that suppress the immune system in the past 6 months, taking strong steroids like prednisone for more than 2 weeks in the last 3 months, or having a nerve disease caused by the immune system.
  • Being allergic (having a systemic hypersensitivity) to any ingredient in the vaccine or having had a life‑threatening allergic reaction to similar products before.
  • Having a long‑term (chronic) illness that the doctor thinks could interfere with taking part in the study or finishing it.
  • Having previously had Guillain‑Barré Syndrome (GBS), a rare condition where the immune system attacks the nerves and can cause weakness.
  • Having already received a vaccine or antibody treatment for RSV or HMPV, including any licensed or experimental vaccine (even if it was a single‑component or combination vaccine) or a monoclonal antibody (a lab‑made protein that targets the virus).
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Investigated drugs

RSV+HMPV protein vaccine (618)
This is a bivalent protein vaccine that contains two experimental proteins, known by the code names VXB-221 and VXB-213. It is given as an injection into the muscle. The vaccine is designed to teach the immune system to recognize and fight two common viruses that cause serious lung infections in older adults: respiratory syncytial virus (RSV) and human metapneumovirus (HMPV). By stimulating the body’s defenses, the vaccine aims to reduce the chance of developing lower‑respiratory‑tract disease (such as pneumonia or bronchitis) caused by these viruses over the following year.

What is already known about the treatment

  • 0.9% NaCL diluent

    This sterile salt‑water solution is given by intramuscular injection and is used only as a placebo in the study. It contains no active drug and is widely recognized as safe and commonly used to match the appearance of real injections. Because it has no therapeutic effect, it has no specific medical indication or mechanism of action. It is classified as a medical diluent or inactive control substance.

  • RSV+HMPV protein vaccine (618)

    The vaccine is administered as a solution for injection given intramuscularly and contains the protein components VXB‑221 and VXB‑213 that target RSV and HMPV. It is an experimental product currently in Phase 2b trials, aiming to prevent lower‑respiratory infections caused by these viruses in older adults. The vaccine works by stimulating the body’s immune system to produce antibodies that recognize and neutralize the viral proteins, providing protective immunity. It is classified as a viral protein subunit vaccine, a prophylactic (preventive) medicine.

Investigated diseases

  • Respiratory syncytial virus lower respiratory tract disease

    This condition is caused by infection with respiratory syncytial virus, which initially produces cold‑like symptoms and then spreads to the lower airways. The virus inflames the bronchioles and lung tissue, leading to cough, wheezing, and difficulty breathing. Mucus production increases and can partially block the small airways. The illness often starts with a runny nose and fever before the lower respiratory signs appear. It is most common in young children and older adults, but anyone can be affected. The disease progresses as the infection moves deeper into the lungs, increasing respiratory discomfort.

  • Human metapneumovirus lower respiratory tract disease

    This disorder results from infection with human metapneumovirus, which first causes upper‑respiratory symptoms and then spreads to the lower respiratory tract. Inflammation of the bronchioles and alveoli leads to coughing, shortness of breath, and wheezing. Excess mucus may accumulate, narrowing the airways. The condition often follows an initial sore throat or mild fever. It can affect people of all ages, with children and the elderly being more susceptible. The disease advances as the virus replicates in the lower airways, increasing respiratory irritation.

Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IITrial ID2026-526177-42-00Protocol codeVCA25397Estimated enrolment8 000 patientsSponsorSanofi Vaccines US Inc.

sourced from the EU Clinical Trials Register and site verification

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