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Yellow FeverPhase 2VYF02NCT04942210

Study on an Investigational Yellow Fever Vaccine Compared With YF-VAX in Adults in the USA

A Phase 2 study testing Yellow fever vaccine (produced on serum-free Vero cells) and Yellow fever vaccine in people with Yellow Fever and Healthy Volunteers, run by Sanofi Pasteur, a Sanofi Company at 11 sites in United States.

Active, not recruiting

Under way, not looking for participants. Everyone needed has enrolled. The study is still running.

Official record
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Trial summary

The primary objective of the study is to demonstrate the non-inferiority of the antibody response in terms of seroconversion rate 28 days after vaccine administration of one dose of yellow fever vaccine (vYF) compared to the antibody response after one dose of the YF-VAX control vaccine in yellow fever naïve… Read more about this study

Who is it for?
Ages 18 to 60 yearsHealthy volunteers can take part
Conditions the study is for
Yellow Fever, Healthy Volunteers
What is being tested?
Yellow fever vaccine (produced on serum-free Vero cells) and Yellow fever vaccine
Could I receive a placebo?
No, everyone receives an active treatment
How many people
568 participants
Where
11 sitesUnited States
Study dates
1 Jul 2021to 29 Jun 2027
Phase
Phase 2
Are there results?
Yes, posted in the registrySummary in the doctors' view

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

  • Ages 18 to 60 years
  • All sexes
  • Healthy volunteers accepted
  • Adult

Who may be able to join

  • Aged 18 years to 60 years on the day of inclusion.
  • A female participant is eligible to participate if she is not pregnant or breastfeeding and one of the following conditions applies:
  • Is of non-childbearing potential. To be considered of non-childbearing potential, a female must be postmenopausal for at least 1 year, or surgically sterile.
  • OR Is of childbearing potential and agrees to use an effective contraceptive method or abstinence from at least 4 weeks prior to vaccination until at least 4 weeks after vaccination. A participant of childbearing potential must have a negative highly sensitive pregnancy test (urine or serum as required by local regulation) before any dose of study intervention on Day 1 and will be repeated on Day 29 to confirm the participant is still not pregnant within the 28 days of vaccine administration.
  • Informed consent form has been signed and dated.
  • Able to attend all scheduled visits and to comply with all study procedures.

Who cannot join

  • Known or suspected congenital or acquired immunodeficiency; or receipt of immunosuppressive therapy, such as anti-cancer chemotherapy, or radiation therapy, within the preceding 6 months; or long-term systemic corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks within the past 3 months).
  • Known history of flavivirus infection.
  • Known systemic hypersensitivity to any of the vaccine components, eggs, or history of a life-threatening reaction to the vaccines used in the study or to a vaccine containing any of the same substances.
  • Known history or laboratory evidence of human immunodeficiency virus infection.
  • Known history of hepatitis B or hepatitis C seropositivity
  • Personal or family history of thymic pathology (thymoma, thymectomy, or myasthenia).
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  • Chronic illness that, in the opinion of the Investigator, is at a stage where it might interfere with trial conduct or completion, including malignancy, such as leukemia, or lymphoma.
  • Moderate or severe acute illness/infection (according to Investigator judgment) on the day of vaccination or febrile illness (temperature ≥ 100.4°F). A prospective participant should not be included in the study until the condition has resolved or the febrile event has subsided.
  • Administration of any anti-viral within 2 months preceding the vaccination and up to the 6 weeks following the vaccination
  • Receipt of any vaccine in the 4 weeks preceding the study vaccination or planned receipt of any vaccine in the 4 weeks following the study vaccination except for influenza vaccination, which may be received at least 2 weeks before study vaccines. This exception includes monovalent pandemic influenza vaccines and multivalent influenza vaccines.
  • Previous vaccination against a flavivirus disease at any time including YF with either the study vaccine or another vaccine.
  • Receipt of immune globulins, blood, or blood-derived products in the past 6 months.
  • Participation at the time of study enrollment (or in the 4 weeks preceding the study vaccination) or planned participation during the first year of the 5-year follow-up in another clinical study investigating a vaccine, drug, medical device, or medical procedure. Enrollment in another study after the first year is permitted (starting the first day of Year 2, and onwards), assuming it does not exclude participation in this study
  • Deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized involuntarily.
  • Alcohol, prescription drug, or substance abuse that, in the opinion of the Investigator, might interfere with the study conduct or completion.
  • Identified as an Investigator or employee of the Investigator or study center with direct involvement in the proposed study, or identified as an immediate family member (ie, parent, spouse, natural or adopted child) of the Investigator or employee with direct involvement in the proposed study.
  • Planned travel in a YF endemic country within 6 months of investigational or control vaccine administration.

Trial locations and contacts

11 sites in 1 country.

11 sites in 1 country

United States11 sites

  • Johns Hopkins Bloomberg School of Public Health (JHSPH)- Site Number : 8400004

    Baltimore, Maryland, 21205

  • Harvard University Medical School- Site Number : 8400002

    Boston, Massachusetts, 02115

  • Emory University Decatur- Site Number : 8400005

    Decatur, Georgia, 30030

  • Velocity Clinical Research - Providence Site Number : 8400015

    East Greenwich, Rhode Island, 02818

  • SUNY Upstate Medical University Global Health Institute Site Number : 8400006

    East Syracuse, New York, 13057

  • Velocity Clinical Research- New Orleans Site Number : 8400008

    New Orleans, Louisiana, 70119

  • New York University Langone Medical Center Site Number : 8400013

    New York, New York, 10016

  • Meridian Clinical Research- Site Number : 8400009

    Omaha, Nebraska, 681134

  • Rochester Clinical Research, Inc.- Site Number : 8400010

    Rochester, New York, 14609

  • J Lewis Research Inc- Site Number : 8400012

    Salt Lake City, Utah, 84109

  • Saint Louis University- Site Number : 8400003

    St Louis, Missouri, 63104

Other trials in United States

About this study

Official title: Controlled Study of Immunogenicity and Safety of the Investigational vYF Candidate Vaccine in Comparison to YF-VAX in Adults

The primary objective of the study is to demonstrate the non-inferiority of the antibody response in terms of seroconversion rate 28 days after vaccine administration of one dose of yellow fever vaccine (vYF) compared to the antibody response after one dose of the YF-VAX control vaccine in yellow fever naïve participants.

The secondary objectives of the study are:

  • To describe the immune response to yellow fever in both vaccine groups before and after vYF or YF-VAX administration.
  • To describe the safety profile of vYF vaccine in comparison to the safety profile of the control YF-VAX.
  • To describe the biosafety profile of vYF in comparison to the biosafety profile of the control YF-VAX.
Read the detailed description

The duration of each participant's participation will be approximately 5 years.

Being tested
Yellow fever vaccine (produced on serum-free Vero cells), Yellow fever vaccine
Medical subject headings
Yellow Fever

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

  • Yellow fever vaccine (produced on serum-free Vero cells)Biological

    Powder and diluent for suspension for injection Subcutaneous injection

  • Yellow fever vaccineBiological

    Also called YF-VAX

    Powder and diluent for suspension for injection Subcutaneous injection

Study groups in NCT04942210
Study groupRoleWhat they receive
vYFExperimental1 injection of vYF at Day 1
Receives: Biological: Yellow fever vaccine (produced on serum-free Vero cells)
YF-VAXActive comparator1 injection of YF-VAX at Day 1
Receives: Biological: Yellow fever vaccine

What is being measured

The primary outcome is the main question the study is designed to answer.

  1. Percentage of Yellow Fever (YF)-Naive Participants Who Achieved Seroconversion 28 Days Post Dose 1

    Seroconversion was defined as a 4-fold increase in Nab titers as compared to the pre-vaccination value. YF-naive participants (or negative) at baseline corresponded to participants with no detectable YF antibody (Ab) titers before vaccination. The YF NAb titers were determined using a validated live virus microneutralization (MN) assay. Percentages are rounded off to the tenth decimal place.

    Measured: 28 days post dose 1 (Day 29)

Secondary outcomes (13)

  1. Percentage of Participants Who Achieved Seroconversion

    Seroconversion was defined as a 4-fold increase in Nab titers as compared to the pre-vaccination value: compared to the Day 1 titers at each timepoint up to Month 6; and to the last planned previous timepoint from Year 1 onwards. The YF NAb titers were determined using a validated live virus MN assay. Percentages are rounded off to the tenth decimal place.

    Measured: Days 1, 11, 29, Month 6, Years 1 and 2

  2. Percentage of Participants Who Achieved Seroprotection

    Seroprotection was defined as NAb titers >=threshold of 10 (1/dilution). The YF NAb titers were determined using a validated live virus MN assay. Percentages are rounded off to the tenth decimal place.

    Measured: Days 1, 11, 29, Month 6, Years 1 and 2

  3. Geometric Mean Titers (GMTs) of Antibodies Against Yellow Fever Virus

    GMTs of antibody against YF virus was measured using a validated live virus MN assay.

    Measured: Days 1, 11, 29, Month 6, Years 1 and 2

  4. Geometric Mean Titers Ratio (GMTRs) of Antibodies Against Yellow Fever Virus

    GMTs of antibody against YF virus was measured using a validated live virus MN assay. Ratio was calculated as post-vaccination titer at Days 11, 29 and Month 6 to pre-vaccination titer at Day 1; post-vaccination titer at Year 1 to pre-vaccination titer at Month 6; post-vaccination titer at Year 2 to pre-vaccination titer at Year 1.

    Measured: Days 1, 11, 29, Month 6, Years 1 and 2

  5. Number of Participants With Unsolicited Systemic Adverse Events (AEs)

    An unsolicited AE was an observed AE that did not fulfill the conditions of solicited reactions, ie, pre-listed in the CRF in terms of diagnosis and onset window post-vaccination.

    Measured: Up to 30 minutes post vaccination on Day 1

  6. Number of Participants With Solicited Injection Site Reactions

    A solicited reaction was an "expected" adverse reaction (AR) (sign or symptom) observed and reported under the conditions (nature and onset) pre-listed in the protocol and CRF. An injection site reaction was an AR at and around the injection site of the study vaccine.

    Measured: Up to 7 days post vaccination (Day 8)

  7. Number of Participants With Solicited Systemic Reactions

    A solicited reaction was an "expected" AR (sign or symptom) observed and reported under the conditions (nature and onset) pre-listed in the protocol and CRF. Solicited systemic reactions were systemic AEs observed and reported under the conditions (nature and onset) pre-listed in the protocol and CRF.

    Measured: Up to 14 days post vaccination (Day 15)

  8. Number of Participants With Unsolicited Adverse Events

    An unsolicited AE was an observed AE that did not fulfill the conditions of solicited reactions, ie, pre-listed in the CRF in terms of diagnosis and onset window post-vaccination.

    Measured: Up to 28 days post vaccination (Day 29)

  9. Number of Participants With Serious Adverse Events (SAEs) and Adverse Events of Special Interest (AESIs) up to 6 Months Post-Vaccination

    An SAE was any AE that at any dose resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, was a congenital anomaly/birth defect, or was an important medical event. An AESI (serious or non-serious) was defined as one of scientific and medical concern specific to the Sponsor's study intervention or program, for which ongoing monitoring and rapid communication by the Investigator to the Sponsor could be appropriate. AESIs included serious hypersensitivity/allergic reactions, organ failure/serious viscerotropic events, serious neurologic events.

    Measured: From the first dose of study vaccine administration (Day 1) up to 6 months post vaccination, approximately up to Day 181

  10. Number of Participants With Serious Adverse Events and Deaths up to Day 1155

    An SAE was any AE that at any dose resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, was a congenital anomaly/birth defect, or was an important medical event.

    Measured: From the first dose of study vaccine administration (Day 1) up to DBL date of 29 August 2024, approximately up to Day 1155

  11. Number of Participants With Serious Adverse Events and Deaths Up to Year 5

    An SAE was any AE that at any dose resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, was a congenital anomaly/birth defect, or was an important medical event.

    Measured: From the first dose of study vaccine administration (Day 1) up to end of study, approximately 5 years

  12. Number of Participants With Out-of-Range Biochemistry Parameters

    Blood samples were collected at specified timepoints for assessment of biochemistry parameters: alanine aminotransferase (ALT), aspartate transaminase (AST), creatine phosphokinase (CPK), alkaline phosphatase (ALP), bilirubin (accompanied by any increase in liver function test (LFT) and normal LFT), creatinine and C-reactive protein (CRP). The intensity grading scale for laboratory abnormalities was pre-specified in the protocol. Number of participants with out-of-range biochemistry parameters are presented.

    Measured: Days 1 and 11

  13. Number of Participants With Out-of-Range Hematology Parameters

    Blood samples were collected at specified timepoints for assessment of hematology parameters: red blood cell count (RBC), hematocrit, mean corpuscular volume (MCV), monocytes, basophils, hemoglobin (Hb), white blood cell count (WBC) (increase and decrease), neutrophils and lymphocytes (decrease), eosinophils, platelets (decrease). The intensity grading scale for laboratory abnormalities was pre-specified in the protocol. Number of participants with out-of-range hematology parameters are presented.

    Measured: Days 1 and 11

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

  1. First posted28 Jun 2021
  2. Study start1 Jul 2021
  3. Primary completion24 Jun 2022
  4. Study completion29 Jun 2027 (estimated)

Resources

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design
Study type
Interventional
Phase
Phase 2
Primary purpose
Prevention
Allocation
Randomised
Intervention model
Parallel groups
Masking
Quadruple blind
Who is masked
Participant, Care provider, Investigator, Outcomes assessor
Enrolment
568 participants (actual)
IDs, dates and publications
ClinicalTrials.gov ID
NCT04942210
Sponsor's protocol ID
VYF02
Other IDs
U1111-1261-5612, VYF02
Acronym
VYF02
Status last verified
Aug 2026
First submitted
25 Jun 2021
Last updated
3 Sep 2026
Data monitoring committee
Yes
FDA-regulated drug
Yes
FDA-regulated device
No
Individual data sharing
Yes: Qualified researchers may request access to patient level data and related study documents including the clinical study report, study protocol with any amendments, blank case report form, statistical analysis plan, and dataset specifications. Patient level data will be anonymized and study documents will be redacted to protect the privacy of trial participants. Further details on Sanofi's data sharing criteria, eligible studies, and process for requesting access can be found at: https://vivli.org

Publications

  • Feroldi E, Mulligan MJ, Talaat KR, Tan CS, Paolino K, Edupuganti S, Collins MH, George SL, Davis M, Essink B, Jeanfreau R, Peterson J, Fried D, Minutello AM, Orlando S, Korejwo J, Rojas A, Dufournet M, Machabert T, Devlin L, Frago C; vYF Vaccine Study Team. Immunogenicity and Safety of vYF, a Yellow Fever Vaccine - A Phase 2 Trial. N Engl J Med. 2026 Apr 9;394(14):1399-1408. doi: 10.1056/NEJMoa2505665.

    PubMed 41950474

Questions about this trial

What is this clinical trial studying?

A Phase 2 study testing Yellow fever vaccine (produced on serum-free Vero cells) and Yellow fever vaccine in people with Yellow Fever and Healthy Volunteers, run by Sanofi Pasteur, a Sanofi Company at 11 sites in United States.

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

The sponsor lists 6 inclusion and 17 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: under way, not looking for participants, as of the sponsor's last update on 3 Sep 2026. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 11 sites in United States. Whether a site is taking part right now should be confirmed with that site. See every site.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

What does this phase mean?

Phase 2 studies give the treatment to a larger group to see whether it has the intended effect and to keep checking safety.

Not every study follows the same path, and some studies (observational studies, device studies) have no phase.

Are results available for this study?

Yes. Results are posted in the registry (first posted 18 Jun 2025). A summary is in the For doctors view, and the full results are on ClinicalTrials.gov.

How can a doctor refer a patient or contact the research team?

The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

Percentage of Yellow Fever (YF)-Naive Participants Who Achieved Seroconversion 28 Days Post Dose 1 (time frame: 28 days post dose 1 (Day 29)). It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT04942210, which also lists 1 linked publication.

Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 3 Sep 2026.

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