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Clesrovimab vs Sodium Chloride for Reducing RSV and Other Respiratory Pathogen Shedding in Healthy Infants

Registered drug
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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 infants at risk for Respiratory Syncytial Virus (RSV), a common virus that can cause serious breathing problems in young children. The investigational product is a medication called clesrovimab, given as an injection. Some participants will receive a simple salt water injection that does not contain the active medicine, serving as a comparison.

The purpose of the study is to see whether giving clesrovimab can reduce the amount of RSV and other germs that are found in the back of the nose and throat. Infants will be randomly assigned to receive either the medication or the comparison injection, and they will be visited several times over a few months. During these visits, a small swab will be taken from the nose to test for virus using a laboratory method called RT-PCR, which looks for the virus’s genetic material, and to examine the community of bacteria with a technique called 16S rRNA sequencing, which identifies the types of microbes present. The study will also track any illnesses such as bronchiolitis, pneumonia, ear infections, or wheezing, as well as any doctor visits or hospital stays.

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

    Enrollment and Consent

    You are asked to read and sign an information form that explains the purpose of the study and what will be required of you.

    Your agreement is recorded before any study procedures begin.

  2. Step 2

    Randomization and Injection

    You are randomly assigned to receive either the study medication or a placebo.

    If you are assigned to the study medication, you will receive clesrovimab at a dose of 105 mg given by intramuscular injection.

    If you are assigned to the placebo, you will receive sodium chloride solution (0.7 ml) by intramuscular injection.

    The injection is administered as a single dose on the day you join the trial.

  3. Step 3

    Baseline Nasopharyngeal Sample Collection

    Immediately after the injection, a healthcare professional will collect a nasopharyngeal swab – a gentle sample taken from the back of your nose.

    The sample is tested using RT‑PCR (reverse transcription polymerase chain reaction) to detect respiratory syncytial virus (RSV) and other viruses or bacteria.

  4. Step 4

    Scheduled Follow‑Up Visits

    You will attend follow‑up visits at the times specified in the study schedule.

    At each visit a nasopharyngeal swab will be taken to monitor the presence and amount of RSV and other respiratory pathogens.

    Your health status, including any fever, cough, or breathing difficulties, will be recorded by study staff.

    If needed, additional samples may be analyzed with 16S rRNA sequencing to study the composition of bacteria in the nasal area.

  5. Step 5

    Final Assessment

    At the end of the study period you will have a final visit that includes one last nasopharyngeal swab.

    All collected data will be used to evaluate how the medication affected RSV shedding, other infections, and the nasal microbiome.

    You will be thanked for completing the study.

Who can join the trial?

6 criteria

  • Infants must be between birth and 12 months old at the time they join the study and must not qualify for the existing Greek RSV vaccine program.
  • The baby must have been born after at least 32 weeks of pregnancy (gestational age), whether full‑term or preterm.
  • The baby must not have received any RSV monoclonal antibody (a lab‑made protein that protects against RSV) or any other RSV preventive medicine in the past six months.
  • The mother must not have been given an RSV vaccine during pregnancy within the last six months.
  • The parent(s) or legal guardian must be willing to sign a written informed consent form and follow all study procedures.
  • The baby must be able to stay in the study for the entire follow‑up period, and the parent(s) must be reachable by telephone throughout the study.

Who cannot join the trial?

15 criteria

  • Having major congenital anomalies (big physical problems present at birth) or known chromosomal abnormalities (abnormalities in the genetic material).
  • Having serious coagulation abnormalities or other bleeding disorders that could make an intramuscular (into the muscle) injection unsafe.
  • Having an acute febrile illness (fever) or any other acute infection at the time of enrollment that would require delaying the study drug.
  • Having any other serious acute or chronic medical condition, a clearly abnormal lab test, or any situation the doctor thinks could increase the risk of participation or interfere with the study procedures.
  • Planning to receive another RSV monoclonal antibody (a lab‑made protein that fights RSV) during the study period.
  • Planning to join another interventional clinical trial (a study testing a new treatment) while taking part in this study.
  • Being an infant whose parents or legal guardians are members of the study team or directly involved in running or evaluating the study.
  • Having a known or suspected primary or secondary immunodeficiency (a condition where the immune system does not work properly).
  • Having severe chronic lung disease that requires supplemental oxygen therapy (extra oxygen support).
  • Having cyanotic congenital heart disease (a heart defect present at birth that causes low oxygen levels in the blood).
  • Having a known or suspected neuromuscular disease (a disorder affecting nerves and muscles).
  • Being hospitalized at the time of enrollment for a condition that requires care in an intensive care unit (a special hospital area for very sick patients).
  • Having already received, or being eligible to receive, nirsevimab (another RSV‑preventing medicine) under the Greek National Immunisation Programme for the current RSV season.
  • Being younger than 6 months whose mother received an RSV vaccine during pregnancy.
  • Having a severe allergic (hypersensitivity) or anaphylactic (life‑threatening allergic) reaction to clesrovimab or any excipient (inactive ingredient) of the study drug.
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Investigated drugs

Clesrovimab is a laboratory‑made antibody that is given by injection into the muscle. It is designed to give infants temporary protection against the respiratory syncytial virus (RSV) and may also affect other germs that live in the nose and throat. In the trial the medicine is being tested to see if it can lower the amount of RSV and other viruses or bacteria that infants carry and spread, and whether it changes the community of harmless bacteria in the nose.

What is already known about the treatment

  • Sodium Chloride Injection/ DEMO 0,9% w/v

    This medication is a sterile solution for injection that is given by intramuscular (muscle) injection. It is widely used in medicine as an electrolyte replacement and also serves as a placebo in clinical studies. It helps restore the body’s normal salt and water balance by providing sodium and chloride ions. It is classified as an electrolyte solution (ATC code B05XA03).

  • Enflonsia 105 mg solution for injection in pre-filled syringe

    This medication is a clear solution for injection that is administered by intramuscular (muscle) injection using a pre‑filled syringe. It is an approved monoclonal antibody used to prevent respiratory syncytial virus (RSV) infection in infants. It works by attaching to the RSV virus and blocking it from entering cells, which stops the virus from multiplying. It belongs to the class of viral‑targeting monoclonal antibodies (ATC code J06BD10).

Investigated diseases

Respiratory syncytial virus infection - Respiratory syncytial virus infection is a common viral illness that primarily affects the nose, throat, and lungs of infants and young children. The virus spreads through droplets when an infected person coughs or sneezes. Initial symptoms often include runny nose, cough, and mild fever. In some cases the infection moves down into the small airways, leading to inflammation and swelling that can cause wheezing and difficulty breathing. This lower‑airway involvement may develop into bronchiolitis or pneumonia, which can last several days to weeks. The illness usually improves as the immune system clears the virus, although the virus can be detected in the nose for a period after symptoms resolve.
Trial detailsLast updated 21 Oct 2026
Age0-17PhasePhase IIITrial ID2026-526874-18-00Protocol codeRSV-SHIELDEstimated enrolment162 patients

sourced from the EU Clinical Trials Register and site verification

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