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Study Comparing the Safety and Immune Response of the Investigational vYF Vaccine and Stamaril for Yellow Fever in Adults in Europe and Asia

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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 Yellow Fever, a viral infection that can cause serious illness. The study is comparing two vaccines: the investigational vYF vaccine and the already available Stamaril vaccine. Both vaccines are designed to protect against Yellow Fever by helping the body build immunity to the virus.

The purpose of the study is to compare the immune response generated by the vYF vaccine to that of the Stamaril vaccine. Participants will receive one dose of either the vYF vaccine or the Stamaril vaccine. The study will monitor the participants' immune response over time, specifically looking at how well their bodies produce antibodies, which are proteins that help fight infections. The study will also track any side effects or reactions to the vaccines.

Participants in the study will be observed for a period of time to assess the effectiveness and safety of the vaccines. This includes checking for any immediate reactions after vaccination and monitoring for any side effects over the following months. The study aims to ensure that the new vYF vaccine is as effective and safe as the existing Stamaril vaccine in providing protection against Yellow Fever.

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

    Initial vaccination

    On the first day of the study, you will receive a single dose of either the investigational vYF vaccine or the control vaccine called Stamaril. Both vaccines are administered as an injection under the skin, known as subcutaneous use.

    The purpose of this step is to evaluate the body's immune response to the vaccine, specifically looking at the production of antibodies against yellow fever.

  2. Step 2

    Monitoring period

    After receiving the vaccine, you will be observed for any immediate reactions for 30 minutes. This is to ensure your safety and to monitor for any potential side effects.

    You will be asked to report any symptoms or reactions you experience after the vaccination, such as pain at the injection site, fever, headache, or muscle aches.

  3. Step 3

    Follow-up visit

    Approximately 28 days after the vaccination, you will return for a follow-up visit. During this visit, a blood sample will be taken to measure the level of antibodies in your blood.

    This step is crucial to determine if the vaccine has successfully triggered an immune response, which is indicated by a significant increase in antibody levels.

  4. Step 4

    Extended follow-up

    You will have additional follow-up visits scheduled at various intervals, including 6 months, 1 year, and annually up to 5 years after the initial vaccination.

    These visits will involve blood tests to monitor the long-term immune response and to ensure continued protection against yellow fever.

  5. Step 5

    Reporting adverse events

    Throughout the study, you are encouraged to report any adverse events or side effects you experience. This includes any unexpected symptoms or health issues that arise during the trial period.

    The information collected will help assess the safety of the vaccine and identify any potential risks associated with its use.

Who can join the trial?

6 criteria

  • Must be between 18 and 60 years old. This means you can join from your 18th birthday until the day before your 60th birthday.
  • Must be able to attend all scheduled visits and follow all study procedures.
  • If you are a female who can have children, you must have a negative pregnancy test before receiving the vaccine on Day 1. The test will be repeated on Day 29 to ensure you are still not pregnant within 28 days of getting the vaccine.
  • If you are a female, you must not be pregnant or breastfeeding. You must either be unable to have children (for example, postmenopausal for at least 1 year or surgically sterile) or agree to use an effective birth control method or abstain from sex starting at least 4 weeks before getting the vaccine until at least 4 weeks after. Note: For French participants, contraception must be used for 12 weeks after getting the vaccine.
  • You must sign and date an informed consent form. If you are under 21 years old in Singapore, your parent(s) or another legally acceptable representative must also sign and date the form.
  • If you are part of the additional group in Asian countries, you must have at least one biological parent of Chinese origin, which you will report yourself.

Who cannot join the trial?

7 criteria

  • Participants who have had a previous vaccination against yellow fever cannot join the study. Yellow fever is a viral infection spread by mosquitoes.
  • Individuals with a known allergy to any component of the vaccine will be excluded. An allergy is when your body reacts negatively to a substance.
  • People with a weakened immune system cannot participate. The immune system is the body's defense against infections.
  • Pregnant or breastfeeding women are not allowed to join the study.
  • Participants with a history of severe reactions to vaccines will be excluded. A severe reaction is a strong negative response to a vaccine.
  • Individuals currently participating in another clinical trial cannot take part in this study.
  • Anyone with a serious illness that requires ongoing medical treatment will be excluded. A serious illness is a health condition that significantly affects your daily life.
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Investigated drugs

  • vYF

    is an investigational vaccine being tested in this clinical trial. It is designed to help the body build immunity against yellow fever, a viral infection transmitted by mosquitoes. The vaccine works by stimulating the immune system to produce antibodies, which are proteins that can recognize and fight the yellow fever virus if the person is exposed to it in the future. In this study, the effectiveness of vYF is being compared to another vaccine to see if it provides a similar level of protection.

  • Stamaril®

    is a vaccine used as a control in this clinical trial. It is an established vaccine that helps protect against yellow fever by prompting the immune system to produce antibodies against the virus. Stamaril® is used as a benchmark in the study to compare the immune response it generates with that of the investigational vaccine, vYF. This comparison helps researchers determine if the new vaccine is as effective as the existing one in preventing yellow fever.

What is already known about the treatment

vYF Candidate Vaccine – This investigational vaccine is administered as a single injection to help protect against yellow fever, a viral infection spread by mosquitoes. Currently, it is being studied in clinical trials to compare its effectiveness and safety to an existing vaccine called Stamaril. The main goal is to see if the vYF vaccine can produce a similar immune response, measured by the production of antibodies, as the Stamaril vaccine. The vYF vaccine works by stimulating the body's immune system to recognize and fight the yellow fever virus, potentially preventing the disease.

Investigated diseases

Yellow fever – Yellow fever is a viral infection transmitted by mosquitoes, primarily found in tropical and subtropical areas of Africa and South America. The disease begins with symptoms such as fever, chills, loss of appetite, nausea, muscle pains, and headaches. As the disease progresses, some individuals may experience a brief recovery period followed by a return of fever, abdominal pain, and liver damage, which can lead to jaundice. In severe cases, bleeding from the mouth, nose, eyes, or stomach may occur. The virus affects the liver and kidneys, potentially leading to organ failure. The progression of yellow fever varies, with some individuals recovering completely while others may experience more severe symptoms.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IITrial ID2022-502047-35-00Protocol codeVYF03Estimated enrolment690 patientsSponsorSanofi Pasteur

sourced from the EU Clinical Trials Register and site verification

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