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Study on the Safety and Effectiveness of Nirmatrelvir and Ritonavir for Nonhospitalized Children with COVID-19 at Risk of Severe Illness

Verified siteInvestigationalNo placebo
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What is this trial about?

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

This clinical trial is focused on studying the treatment of COVID-19 in children who are not hospitalized but have symptoms and are at risk of developing severe illness. The study involves the use of a medication combination called nirmatrelvir and ritonavir, which are taken orally. Nirmatrelvir is also known by its code name PF-07321332. The purpose of the study is to understand how these medications work in children and to determine the right dose for different age groups, ensuring it is safe and well-tolerated.

Participants in the study will take the medication for a short period, up to five days. The study will monitor how the body processes the medication and check for any side effects. The study will also look at how well the medication works in reducing the risk of severe illness from COVID-19. Children from birth to under 18 years old who have tested positive for COVID-19 and show symptoms can be part of this study.

The study will collect information on the safety of the medication and how it affects the virus in the body. It will also assess how easy and pleasant it is for children to take the medication, which comes in the form of tablets or oral powder. The goal is to find a treatment that can help prevent severe COVID-19 in children who are at higher risk due to underlying health conditions.

The research process

The trial runs in 4 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Enrollment

    Upon joining the study, confirmation of a positive SARS-CoV-2 infection is required. This is typically done through a test like RT-PCR, which detects the virus in the body.

    Participants must show symptoms of COVID-19 and have at least one risk factor for severe illness, such as being overweight, having a chronic condition, or being under one year of age.

  2. Step 2

    Medication administration

    The study involves taking two medications: nirmatrelvir and ritonavir. These are administered orally, meaning they are taken by mouth.

    The form of the medication may vary, including tablets or oral powder in a sachet. The specific form and dosage depend on the participant's age and weight.

  3. Step 3

    Monitoring and assessments

    Throughout the study, regular monitoring is conducted to assess the safety and effectiveness of the medications. This includes checking for any side effects and measuring vital signs.

    Participants may undergo tests to measure the amount of the virus in their body over time, using methods like nasal swabs.

  4. Step 4

    Follow-up

    The study includes follow-up assessments to track the participant's health and any potential hospitalizations or severe outcomes related to COVID-19.

    Feedback on the acceptability and taste of the medications is also collected to improve future formulations.

Who can join the trial?

25 criteria

  • Participants can be male or female.
  • Participants are divided into different groups based on age and weight:
    • Cohort 1: Ages 12 to less than 18 years, weighing 40 kg or more.
    • Cohort 2: Ages 6 to less than 18 years, weighing 20 kg to less than 40 kg.
    • Cohort 3: Ages 2 to less than 6 years.
    • Cohort 4: Ages 1 month (28 days) to less than 2 years.
    • Cohort 5: From birth (44 weeks postmenstrual age) to less than 1 month, weighing more than 2.6 kg.
    • Female participants who can have children must have a negative urine pregnancy test.
    • Female participants who can have children must agree to use a highly effective method of birth control for at least 28 days after the last dose of the study medication if there is a risk of pregnancy.
    • Participants in Cohorts 1 and 2 must be able to swallow tablets until an oral powder form is available.
    • Participants must have a confirmed **SARS-CoV-2 infection** (the virus that causes COVID-19) through a test like **RT-PCR** or another approved method within 72 hours before joining the study.
    • Participants must have shown signs or symptoms of COVID-19 within 5 days before joining the study and have at least one symptom on the day of joining.
    • Participants must have at least one condition that increases the risk of severe COVID-19, such as:
      • Being overweight or obese.
      • Being a current smoker.
      • Having an **immunosuppressive disease** (a condition where the immune system is weakened) or taking medications that weaken the immune system.
      • Having a chronic lung disease, like asthma that requires daily treatment.
      • Having high blood pressure (hypertension).
      • Having heart disease.
      • Having diabetes (Type 1 or Type 2).
      • Having chronic kidney disease.
      • Having sickle cell disease.
      • Having **neurodevelopmental disorders** (conditions affecting brain development) or other complex medical conditions.
      • Having active cancer, except for localized skin cancer.
      • Being an infant (less than 1 year old).
      • Having a spinal cord injury.
      • Any new risk factors for severe COVID-19 identified by health authorities for children.
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Investigated drugs

  • Nirmatrelvir

    is a medication being studied for its ability to treat COVID-19 in children who are showing symptoms and are at risk of developing severe illness. It is taken by mouth and works by helping to stop the virus from multiplying in the body, which may help reduce the severity of the disease.

  • Ritonavir

    is used in combination with nirmatrelvir to enhance its effectiveness. Ritonavir helps increase the levels of nirmatrelvir in the body, allowing it to work better against the virus. This combination aims to provide a safe and effective treatment option for children with COVID-19 who are not hospitalized but are at risk of severe disease progression.

What is already known about the treatment

Nirmatrelvir/Ritonavir – This medication is administered orally and is currently being studied in clinical trials for its safety, pharmacokinetics, and efficacy in treating nonhospitalized pediatric patients with COVID-19 who are at risk of severe disease progression. It is an investigational treatment for SARS-CoV-2 infection, aiming to provide therapeutic benefits by inhibiting viral replication. Nirmatrelvir works by blocking a key enzyme the virus needs to multiply, while Ritonavir boosts the effectiveness of Nirmatrelvir by slowing its breakdown in the body. This combination is classified as an antiviral therapy and is being evaluated to ensure it achieves the desired drug levels in children similar to those in adults.

Investigated diseases

COVID-19 – COVID-19 is an infectious disease caused by the SARS-CoV-2 virus. It primarily spreads through respiratory droplets when an infected person coughs, sneezes, or talks. The disease can range from mild symptoms like fever, cough, and fatigue to more severe respiratory issues. Some individuals may experience loss of taste or smell, muscle aches, and sore throat. In severe cases, it can lead to pneumonia and difficulty breathing. The progression of the disease varies, with some people recovering quickly while others may experience prolonged symptoms.
Trial detailsLast updated 7 Oct 2026
Age0-17PhasePhase IVTrial ID2023-509773-23-00Protocol codeC4671026Estimated enrolment158 patientsSponsorPfizer Inc.

sourced from the EU Clinical Trials Register and site verification

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