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Study on the Safety of a New Chickenpox Vaccine (GSKVX000000025896) Compared to Varicella Virus Oka/Merck Strain in Healthy Children Aged 12-15 Months

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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 safety of a new vaccine for chickenpox, also known as varicella. The trial involves healthy children aged 12 to 15 months. The investigational vaccine, referred to by its code name GSKVx000000026768, will be compared to an existing vaccine called Varivax. Both vaccines are designed to protect against chickenpox, a common childhood illness that causes an itchy rash and fever.

The purpose of the study is to evaluate the safety of the new vaccine when given to young children. During the study, children will receive either the investigational vaccine or Varivax. The vaccines will be administered as a single dose through a small injection under the skin, known as a subcutaneous injection. The study will also involve the administration of other routine vaccines, such as the MMR vaccine (measles, mumps, and rubella), the HAV vaccine (hepatitis A), and, if applicable, the PCV (pneumococcal conjugate vaccine).

Throughout the study, researchers will monitor the children for any reactions to the vaccines, such as redness or swelling at the injection site, fever, or rash. These observations will help determine the safety of the new vaccine. The study will last several months, with follow-up visits to check on the children's health and any potential side effects. The goal is to ensure that the new vaccine is safe for use in preventing chickenpox in young children.

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

    Joining the study

    Upon joining the study, the parent or legal representative of the participant provides written or witnessed consent. This consent is necessary before any study-specific procedures can begin.

    The participant must be a healthy child between 12 to 15 months of age, as determined by a medical history review and clinical examination.

  2. Step 2

    Receiving the vaccine

    The participant will receive a dose of the investigational varicella vaccine or the Varivax vaccine. This is administered as a suspension for injection under the skin, known as a subcutaneous injection.

    The vaccine is given as a first dose to healthy children within the specified age range.

  3. Step 3

    Monitoring for reactions

    After receiving the vaccine, the participant will be monitored for any reactions at the injection site for up to 4 days.

    Systemic events, which are reactions that affect the whole body, will be observed for up to 15 days. Fever will be specifically monitored for up to 22 days.

    Any rash or other systemic events will be monitored for up to 43 days after the vaccine is given.

  4. Step 4

    Reporting any adverse events

    Any unexpected reactions or adverse events will be recorded for up to 43 days after the vaccine is administered.

    Medically attended adverse events, which require medical attention, will be monitored until the end of the study, which is estimated to be 181 days after the vaccine is given.

  5. Step 5

    Study completion

    The study is expected to conclude by December 5, 2025. During this time, all data collected will be used to evaluate the safety of the investigational vaccine compared to the Varivax vaccine.

Who can join the trial?

5 criteria

  • The participant's parent(s) or legal representative(s) must be able and willing to follow the study rules, like filling out electronic diaries and coming back for follow-up visits.
  • Written or witnessed/thumb-printed informed consent must be obtained from the participant's parent(s) or legal representative(s) before any study-specific procedures are done.
  • The participant must be healthy, as determined by their medical history and a physical examination before joining the study.
  • The participant must be a boy or girl aged between 12 to 15 months old. This means from their first birthday until the day before they turn 16 months old at the time of receiving the study vaccines.
  • For children in countries where the Pneumococcal Conjugate Vaccine (PCV) is recommended at 12 to 15 months of age and is part of the study: The participant must have received the primary series of PCV in their first year of life, with the last dose given at least 60 days before joining the study.

Who cannot join the trial?

10 criteria

  • Individuals with a current or past infection of Varicella (also known as chickenpox) cannot participate.
  • Participants who have received any other vaccines within 4 weeks prior to the study cannot join.
  • Anyone with a known allergy to any component of the study vaccines is excluded.
  • Individuals with a weakened immune system, which means their body has a harder time fighting infections, are not eligible.
  • Participants who are currently taking medications that affect the immune system cannot take part.
  • Pregnant or breastfeeding women are not allowed to participate.
  • Anyone with a history of severe reactions to vaccines is excluded.
  • Individuals with any serious chronic illness that could interfere with the study are not eligible.
  • Participants who have participated in another clinical trial within the last 30 days cannot join.
  • Anyone with a history of alcohol or drug abuse within the past year is excluded.
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Investigated drugs

The VNS vaccine is an investigational vaccine being tested in this clinical trial. It is designed to protect against varicella, commonly known as chickenpox, which is a contagious disease that causes an itchy rash and flu-like symptoms. The trial aims to assess the safety of this new vaccine when given to young children, alongside other routine vaccinations.

Varivax is an existing vaccine that is already used to protect against chickenpox. In this trial, it serves as a comparison to the investigational VNS vaccine. By comparing the two, researchers hope to determine if the new vaccine is as safe and effective as the established Varivax vaccine.

The MMR vaccine is a well-known vaccine that protects against three diseases: measles, mumps, and rubella. In this study, it is given alongside the varicella vaccines to see how well the vaccines work together and to ensure that they do not cause any unexpected side effects when administered at the same time.

The HAV vaccine is used to protect against hepatitis A, a liver infection caused by the hepatitis A virus. This vaccine is included in the trial to evaluate its safety and effectiveness when given with the varicella and MMR vaccines.

The PCV, or pneumococcal conjugate vaccine, is used to protect against infections caused by the bacterium Streptococcus pneumoniae, which can lead to serious illnesses like pneumonia, meningitis, and bloodstream infections. In this trial, the PCV is administered if applicable, to assess its safety when given with the other vaccines.

What is already known about the treatment

VNS vaccine – The VNS vaccine is administered as an injection to healthy children aged 12 to 15 months. It is currently being studied in a Phase 3a clinical trial to assess its safety compared to the existing Varivax vaccine. The main therapeutic indication for the VNS vaccine is to prevent varicella, commonly known as chickenpox. At the molecular level, the vaccine works by stimulating the immune system to recognize and fight the varicella-zoster virus, which causes chickenpox. It is classified as a live attenuated vaccine, meaning it contains a weakened form of the virus that cannot cause disease in healthy individuals.

Investigated diseases

Varicella – Varicella, commonly known as chickenpox, is a highly contagious viral infection caused by the varicella-zoster virus. It primarily affects children and is characterized by an itchy, blister-like rash that first appears on the chest, back, and face before spreading to the rest of the body. The rash progresses from red spots to fluid-filled blisters, which eventually crust over and heal. In addition to the rash, symptoms may include fever, fatigue, and headache. The disease spreads through direct contact with the rash or through respiratory droplets from an infected person. After the initial infection, the virus can remain dormant in the body and may reactivate later in life as shingles.
Trial detailsLast updated 2 Oct 2026
Age0-17PhasePhase IIITrial ID2024-515868-31-00Protocol code213997 (VNS 20-001)Estimated enrolment750 patientsSponsorGlaxoSmithKline Biologicals

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