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Safety, Tolerability and Immunogenicity of RSV prefusion F protein 847a and 847b Vaccine in Children 5‑17 Years at High Risk of RSV Disease

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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 preventing lower respiratory tract disease caused by respiratory syncytial virus, a common virus that can lead to serious lung infections, especially in children with chronic health problems. The investigational product is a vaccine called RSVpreF, supplied as a powder that is mixed with a liquid and given by injection into the muscle. The vaccine contains two key components: the virus’s subgroup A prefusion F protein and the virus’s subgroup B prefusion F protein, which are designed to help the immune system recognize and fight the virus. Some participants will receive a matching placebo that looks the same but does not contain the active vaccine ingredients.

The main goal of the trial is to learn whether the vaccine is safe and can produce an immune response in children aged 5 to under 18 who have chronic medical conditions or weakened immune systems. Participants will receive one or two doses of the vaccine (or placebo) and will be monitored for any side effects such as pain at the injection site, fever, or other symptoms, as well as for the body’s production of protective antibodies against the virus. Follow‑up visits will occur over several weeks to check health status and collect blood samples, allowing researchers to compare the vaccine’s effects with those seen in older adults.

The research process

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

Step 1
Baseline visit and first injection
At the first clinic visit after joining the study, personal health information and a small amount of blood are collected to establish a starting point for safety and immune‑response measurements.
The study medication, called Abrysvo vaccine, is given as a single intramuscular injection containing a dose of 120 µg of the vaccine ingredients.
The injection may be the active vaccine or a matching placebo, depending on the study assignment.
Step 2
Immediate observation after injection
After the injection, you remain in the clinic for a short period (typically about 30 minutes) while staff watch for any immediate local reactions such as pain, redness, or swelling at the injection site, and for any rapid systemic events such as fever.
Step 3
Home monitoring of symptoms
For several days following the injection, you keep track of any new or worsening symptoms, including:
local reactions (pain, redness, swelling),
systemic events (fever, vomiting, diarrhea, headache, fatigue or tiredness, muscle pain, joint pain),
And any other health changes that feel unusual.
You record these observations in a diary or on the study form provided.
Step 4
First follow‑up visit
A scheduled clinic visit occurs a few days to weeks after the first injection.
During this visit, staff review the symptom diary, check for any adverse events (health problems that may be related to the study medication), and collect another small blood sample to begin measuring the immune response.
Step 5
Possible second injection
Depending on the specific study group, a second intramuscular injection of the same vaccine (again 120 µg) may be administered after a defined interval.
The same procedures of observation, home monitoring, and follow‑up visits are repeated after this second dose.
Step 6
Final study visit and end of participation
At the last clinic visit, a final health assessment is performed, including collection of a blood sample to evaluate the overall immune response and to check for any late‑occurring adverse events.
After this visit, all study activities for you are completed.

Who can join the trial?

6 criteria

Age: Be between 5 and 18 years old at the time of the first study visit.
Health condition: Have a chronic medical condition (a long‑lasting health problem) or an immunocompromising condition (a condition that weakens the body’s ability to fight infections), depending on which study group you are placed in.
High risk for RSV: Be considered at high risk for a lower respiratory tract infection caused by respiratory syncytial virus (RSV), meaning you are more likely than most children to get a serious lung infection from this virus.
Informed consent: Have a parent or legal guardian who can sign the informed consent form, which explains the study and agrees to follow its rules.
Assent: Be able to give assent (a child’s agreement) in a way that is appropriate for your age, either by speaking or signing, if required by local rules.
Study participation: Be willing to attend the required study visits and follow the study procedures.

Who cannot join the trial?

8 criteria

People who have a weakened immune system (immunocompromised) because of a known or suspected immune deficiency, based on their medical history or test results.
People who have had an autoimmune disease (a condition where the body attacks itself) that required treatment, such as systemic lupus erythematosus. (Stable type 1 diabetes and hypothyroidism are allowed.)
People who have experienced a serious bad reaction to a vaccine before, or who have a severe allergy (anaphylaxis – a sudden, life‑threatening allergic reaction) to any part of the study vaccine.
People with a bleeding problem (bleeding diathesis) that causes prolonged bleeding and would make a muscle shot (intramuscular injection) unsafe.
People who have uncontrolled epilepsy or other seizure disorders, or who have had seizures or other nerve problems after a vaccine.
People who have had Guillain‑Barré syndrome (a rare nerve disorder) or acute polyneuropathy (sudden damage to many nerves) without a known cause.
People who are currently pregnant.
People with any medical or mental health condition, including recent thoughts of suicide (active suicidal ideation in the past year) or suicide attempts (suicidal behavior in the past five years), or abnormal lab test results (laboratory abnormality) that the doctor believes make participation unsafe.

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Verified sites

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Fundacion Para La Investigacion Biomedica Del Hospital Universitario La Paz
Responsive
Madrid, Spain
Hospital General Universitario Gregorio Maranon
Verified
Madrid, Spain
Hospital Sant Joan De Deu Barcelona
Verified
Esplugues De Llobregat, Spain

Trial locations

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Investigated drugs

Abrysvo is a vaccine that helps the body build protection against respiratory syncytial virus (RSV), a common virus that can cause serious lung infections in children. The vaccine contains two pieces of the virus—one from subgroup A and one from subgroup B—designed to look like the part of the virus that triggers the strongest immune response. It is given as an injection into the muscle. In this study, the vaccine is being tested in children ages 5 to under 18 who have chronic health problems or weakened immune systems. Researchers are checking how safe and well‑tolerated the vaccine is, and how well it stimulates the immune system compared with the response seen in older adults. The goal is to see if the vaccine can safely protect these high‑risk children from RSV disease.

What is already known about the treatment

Abrysvo - The vaccine is supplied as a liquid that is injected into the muscle (intramuscular). It is an approved recombinant subunit vaccine that is widely studied and documented in medical literature for preventing RSV disease. It is used to protect against lower‑respiratory‑tract illness caused by respiratory syncytial virus. The product contains two stabilized prefusion F proteins from RSV subgroups A and B, which stimulate the immune system to make antibodies that block the virus, and it is classified as a viral vaccine.

Investigated diseases

Respiratory syncytial virus lower respiratory tract infection - Respiratory syncytial virus lower respiratory tract infection is a viral illness that affects the bronchi and lungs, especially in children and people with chronic conditions. After the virus is inhaled, it infects the cells lining the airways, causing inflammation and swelling. Initial signs often include runny nose and cough, which can develop into wheezing and difficulty breathing as the infection moves deeper. The inflammation may lead to excess mucus and narrowed airways, making breathing harder. Over days to weeks the infection usually resolves as the immune system clears the virus, though symptoms may linger.