RSV is a common virus that infects most children by the age of 2. The range of symptoms can be mild, such as a cough and runny nose, or more severe causing a lower respiratory tract infection, such as pneumonia or bronchiolitis.

RSV is also the leading cause of pneumonia in young children worldwide. Today, there are no antiviral treatments available to help children infected with RSV.

This clinical trial will help doctors & scientists find the most appropriate dose of a study medicine called sisunatovir, which may help children under 5 years old with pneumonia (lower respiratory tract infection) caused by RSV.

As all parents know, children are our greatest treasure. They are special but vulnerable people who need the best care we can give them. Your child’s safety is the top priority of this clinical trial. Children’s clinical trials have additional safety guidelines. These guidelines are governed by regulatory agencies such as the U.S. FDA. Before your child participates, you will be given all the details about the trial, including potential benefits and risks of taking part. Should you decide to take part, your child will receive care from a team of dedicated healthcare professionals, and their health will be monitored closely by the trial team.

Who may participate

Medicines that we depend on for our children today were only made possible because of the families who decided to join a clinical trial. Thank you for taking the time to learn more.

Your child might be able to take part in this clinical trial if they:

  • Have a positive diagnosis of RSV, with evidence of a lower respiratory tract infection (such as pneumonia or bronchiolitis)
  • Are under 5 years old
  • Weigh between 5.5 lbs and 50 lbs
  • Are otherwise in good health with no significant medical problems

If you decide to learn more, the study team will discuss other requirements with you.

We believe that all children should benefit from new treatments for RSV, that’s why diversity is really important in clinical research. The greater the diversity among clinical trial participants, the more we can learn about potential medicines for RSV, including how they work for children of all races and ethnicities.


Respiratory Syncytial Virus (RSV) infection


1 day up to 60 months (5 years old)

Each clinical study has its own guidelines for who can participate, called eligibility criteria. However, only the research study staff can determine if you qualify to enroll in the study.

What to expect

In this clinical trial, your child will have certain tests, procedures, and activities. What happens at each visit will vary, and the study team will provide you with information on what to expect.

The clinical trial visits may include the following activities:

  • Physical examination
  • Questionnaires
  • Study procedures and tests

This trial is double-blind, which means that neither you nor the trial team will know whether your child is receiving the study medicine or the placebo. A placebo does not have any medicine in it but looks just like the medicine being studied.

Participants will have a 2 in 3 (66%) chance of receiving the study medicine and a 1 in 3 (33%) chance of receiving the placebo.

All participants will continue to receive what doctors call the “standard of care”. This means they will be cared for using the current best practices used to treat children with RSV. No child will be denied the necessary care he or she needs because of their clinical trial participation.

You will be reimbursed for any reasonable expenses that you may have as a result of taking part in this trial. This may include parking, meals, or other travel-related expenses.

Length of study treatment

About 5 weeks

Number of study visits

6 - 7 visits. For your convenience, some visits can be done as a home visit or a telehealth visit using telecommunication technologies

Long-term follow up

28 days

About Respiratory Syncytial Virus (RSV)

child holding a doll – Pfizer Clinical Trials
child holding a doll – Pfizer Clinical Trials

About Respiratory Syncytial Virus (RSV)

RSV (respiratory syncytial virus) is a highly contagious virus. Symptoms can appear like the common cold, or they can be more serious. Infants and older adults are at the greatest risk for developing a severe RSV infection, where RSV may infect the lungs, leading to inflammation, causing pneumonia or bronchiolitis, and making it difficult to breathe. RSV pneumonia may require a stay in hospital, and patients may sometimes need additional oxygen or IV fluids (if they can’t eat or drink enough) while in the hospital.

Frequently asked questions

How long will my child be in the clinical trial?

Your child will be in the trial for about 5 weeks. The treatment period is 5 days and there will be a follow up visit with the study doctor to check on your child’s health about a month after the last dose of study medicine.

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How often will the study medicine be given?

Your child will receive the study medicine for up to 5 days, 2 doses daily approximately every 12 hours or 10 doses in total.

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What are the benefits and risks?

Your child’s health may get better, get worse, or stay the same. Their health will be closely monitored during the trial. Participation may help children in the future by increasing our understanding of the study medicine and lower respiratory tract infection caused by RSV. Every medicine that we depend on for our children today was only made possible because of families like yours, who decided to join a trial.

If your child’s health gets worse, your study doctor will help you decide what to do, which may mean stopping their participation in the trial. Potential risks from taking part in the trial may include: side effects from taking the study medicine, for example, nausea, diarrhea, and abdominal pain, and some that are unknown at this time.

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Which study medicine will my child receive?

Your child will receive either sisunatovir or placebo. Your child will have a 1 in 3 chances of receiving a placebo, and a 2 in 3 chance of receiving sisunatovir.

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What if we’re not sure about the clinical trial?

We understand that making a decision to participate in a clinical trial may be difficult during this time. Please feel free to ask the study doctor any questions you may have. With the support of the study team, you can decide what’s best for your child.

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What safety measures are in place in pediatric clinical research?

In all clinical trials, the researchers must follow guidelines and requirements to protect the participants’ rights, safety, and well-being. Pediatric clinical trials have additional safety guidelines. As with clinical trials with adult participants, the guidelines are governed by regulatory agencies such as the U.S. FDA, and oversight is provided by institutional review boards or independent ethics committees. In addition, the regulatory agencies require pediatric-specific drug development plans that are reviewed and agreed to by the agencies’ pediatric experts.

Pediatric clinical studies are also designed with special considerations for children. For example, needle pokes are minimized when possible. The amount of blood taken during the clinical trial may be limited based on the age of the child.

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