A Phase 3 interventional study of Yellow fever vaccine (live) and Yellow fever vaccine (live) in Yellow Fever Immunization, sponsored by Sanofi. Active, not recruiting at 15 sites in 3 countries. Open to participants aged 9 Months to 5 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-11-05.
Sponsored by Sanofi · Phase 3, Interventional, and Prevention
The purpose of this study is to determine whether vYF (investigational vaccine) is safe and can help the body to develop antibodies (immunogenicity) compared with Stamaril vaccine and YF-VAX vaccine (both licensed vaccines) and when they are co-administered with Measles Mumps Rubella (MMR) vaccines in infants aged 11-15 months.
Number of Participants:
A total of 2440 participants is planned to be enrolled in VYF04 study.
Study Arms and Duration:
Eligible participants will be randomized in 2 independent groups (9-24 months, 2-5 years) to receive 1 dose of either vYF or Stamaril or YF-VAX in a 2:1:1 ratio within each age group. An additional group with participants of 11-15 months of age will also receive at the same vaccination visit vYF and a single dose of MMR vaccine.
For the 2nd step (YF booster vaccine administration in a subset), at the Year (Y) 3 visit, a subset of 120 participants of the 9-24 months of age group who did receive a YF vaccine on Day(D) 01 will be invited to join a booster dose assessment (booster dose administered after the Y3 visit blood sample has been taken). Participants aged 11 to 15 months at the time of the concomitant administration of vYF and MMR will not be eligible for receiving a booster dose.
The duration of each participation will be approximately 3 years for all participants (including participants co-administered on D01 with vYF and MMR), and 6 more months post-booster dose administration for the participants enrolled in the booster subset.
The duration of each participant's participation will be up to approximately 3 years (not including booster phase in a subset)
The Phase III VYF04 is the first study to be carried out with the investigational vYF in pediatric populations.
52 studies on the registry are indexed under Yellow Fever; 10 are open to participants now.
This study's planned enrollment of 2,440 is above the median of 112 across 43 interventional studies indexed under Yellow Fever.
Browse Yellow Fever studies →Sanofi is the lead sponsor of 1,557 studies on the registry; 91 are open to participants now.
Of its 205 completed or terminated interventional studies of FDA-regulated products, 123 (60%) have results posted.
Counted across the registry records on this site, refreshed daily.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Aged 9 months to 5 years on the day of inclusion*
* "9 months to 5 years" means from the day of the 9th month after birth to the day before the 6th year birthday
Aged 11 to 15 months* on the day of inclusion for participants enrolled in the MMR co-administration group
* "11 to 15 months" means from the day of the 11th month after birth to the day before the 16th month birthday
For infants*, born after a gestation period of 27 through 36 weeks and medically stable as assessed by the investigator, based on the following definition: "Medically stable" refers to the condition of premature infants who do not require significant medical support or ongoing management for debilitating disease and who have demonstrated a clinical course of sustained recovery by the time they receive the first dose of study intervention
* Infants aged 9 months to 11 months up to the day before the 12th month birthday
Exclusion Criteria:
Participants are excluded from the study if any of the following criteria apply:
Chronic illness* that, in the opinion of the Investigator, is at a stage where it might interfere with study conduct or completion , including , such as leukemia, or lymphoma
*Chronic illness may include, but is not limited to, cardiac disorders, renal disorders, auto-immune disorders, diabetes, psychiatric disorders or chronic infection
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
Hepatitis B is a virus that infects the liver. These are separate tests: HBsAg positive usually means a current infection (a recent vaccination can briefly cause it too); total anti-HBc (HBcAb) positive means an infection now or in the past; HBV DNA measures how much virus is in the blood.
Some studies accept a past infection if HBV DNA is undetectable, sometimes with antiviral medicine during the study. Check what this study allows.
Hepatitis C is a virus that infects the liver. An HCV antibody test can stay positive after an infection has cleared (and is occasionally positive without one); an HCV RNA test shows whether the virus is there now.
After treatment, hepatitis C counts as cured when HCV RNA is still undetectable 12 weeks or more after the treatment ended. Studies often accept people cured this way.
Immunosuppression
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Corticosteroids (steroids)
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hypersensitivity
An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Cancer (malignancy)
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Investigational drug or device
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
HIV
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hepatitis B tests
Hepatitis B is a virus that infects the liver. These are separate tests: HBsAg positive usually means a current infection (a recent vaccination can briefly cause it too); total anti-HBc (HBcAb) positive means an infection now or in the past; HBV DNA measures how much virus is in the blood.
Some studies accept a past infection if HBV DNA is undetectable, sometimes with antiviral medicine during the study. Check what this study allows.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hepatitis C tests
Hepatitis C is a virus that infects the liver. An HCV antibody test can stay positive after an infection has cleared (and is occasionally positive without one); an HCV RNA test shows whether the virus is there now.
After treatment, hepatitis C counts as cured when HCV RNA is still undetectable 12 weeks or more after the treatment ended. Studies often accept people cured this way.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Primary vaccination phase: 1 injection of vYF vaccine at Day 1 Booster phase: 1 injection of vYF vaccine at Year 3 (in a subset)
Biological: Yellow fever vaccine (live)
Primary vaccination phase: 1 injection of Stamaril vaccine at Day 1 Booster phase: 1 injection of Stamaril vaccine at Year 3 (in a subset)
Biological: Yellow fever vaccine (live)
Primary vaccination phase: 1 injection of YF-VAX vaccine at Day 1 Booster phase: 1 injection of YF-VAX vaccine at Year 3 (in a subset)
Biological: Yellow fever vaccine (live)
Primary vaccination phase: 1 injection of vYF vaccine at Day 1
Biological: Yellow fever vaccine (live)
Primary vaccination phase: 1 injection of Stamaril vaccine at Day 1
Biological: Yellow fever vaccine (live)
Primary vaccination phase: 1 injection of YF-VAX vaccine at Day 1
Biological: Yellow fever vaccine (live)
Primary vaccination phase: 1 injection of MMR vaccine at Day 1 in a cohort of 11 to 15 months of age vaccinated with vYF
Biological: Yellow fever vaccine (live) · Biological: Measles, combinations with mumps and rubella, live attenuated
Powder and diluent for suspension for injection Subcutaneous
Also known as: vYF vaccine
Powder and diluent for suspension for injection Subcutaneous
Also known as: Stamaril vaccine
Powder and diluent for suspension for injection Subcutaneous
Also known as: YF-VAX vaccine
Powder, lyophilized, for suspension for reconstitution Subcutaneous or intermuscular
Also known as: MMR II vaccine
Percentage of participants with seroconversion to YF virus after 1 dose of vYF compared to seroconversion after 1 dose of the Stamaril in YF-naive participants (9-24 months)
Seroconversion rates will be assessed using a YF MN assay Seroconversion is defined as a 4-fold increase in NAb titers as compared to the pre-vaccination value
Time frame: At Day 29, 28 days post-vaccination (on Day 01) with vYF or Stamaril
Percentage of participants with seroconversion to YF virus after 1 dose of vYF compared to seroconversion after 1 dose of the YF-VAX in YF-naive participants (9-24 months)
Seroconversion rates will be assessed using a YF MN assay Seroconversion is defined as a 4-fold increase in NAb titers as compared to the pre-vaccination value
Time frame: At Day 29, 28 days post-vaccination (on Day 01) with vYF or YF-VAX
Percentage of participants with seroconversion to YF virus after 1 dose of vYF compared to seroconversion after 1 dose of the Stamaril in YF-naive participants (2-5 years)
Seroconversion rates will be assessed using a YF MN assay Seroconversion is defined as a 4-fold increase in NAb titers as compared to the pre-vaccination value
Time frame: At Day 29, 28 days post-vaccination (on Day 01) with vYF or Stamaril
Percentage of participants with seroconversion to YF virus after 1 dose of vYF compared to seroconversion after 1 dose of the YF-VAX in YF-naive participants (2-5 years)
Seroconversion rates will be assessed using a YF MN assay Seroconversion is defined as a 4-fold increase in NAb titers as compared to the pre-vaccination value
Time frame: At Day 29, 28 days post-vaccination (on Day 01) with vYF or YF-VAX
Percentage of participants, by age group, with seroconversion to YF virus in all investigational vaccine groups before (Day 01) and after investigational vaccine administration at various timepoints
Seroconversion rates will be assessed using a YF MN assay Seroconversion is defined as a 4-fold increase in NAb titers as compared to the pre-vaccination value
Time frame: At Day 01 and at Day 11 (in a subset), Day 15 (in a subset), Day 29, Month 6, and yearly from Year 1 to Year 3
Percentage of participants, by age group, with seroprotection to YF virus in all investigational vaccine groups before (Day 01) and after investigational vaccine administration at various timepoints
Seroprotection is defined as NAb titers ≥ 10 (1/dil) at the corresponding timepoint
Time frame: At Day 01 and at Day 11 (in a subset), Day 15 (in a subset), Day 29, Month 6, and yearly from Year 1 to Year 3
Geometric Mean Titers (GMTs) of neutralizing antibodies against YF virus in all investigational vaccine groups, by age group, before (Day 01) and after investigational vaccine administration at various timepoints
Antibody titers are expressed as geometric mean titers
Time frame: At Day 01 and at Day 11 (in a subset), Day 15 (in a subset), Day 29, Month 6, and yearly from Year 1 to Year 3
Geometric Mean Titers Ratio (GMTRs) of neutralizing antibodies against YF virus in all investigational vaccine groups, by age group, before (Day 01) and after investigational vaccine administration at various timepoints
At Day 01 and at Day 11 (in a subset), Day 15 (in a subset), Day 29, Month 6, and yearly from Year 1 to Year 3
Time frame: GMTRs Day 11/Day 01 (subset only), Day 15/ D01 (subset only), Day 29/Day 01, Month 6/Day 01, Year 1/Month 6, Year 2/Year 1, Year 3/Year 2
Percentage of participants with seroconversion to YF virus in all investigational vaccine groups 28 days after the co-administration of vYF with measlescontaining vaccine in the MMR group and at successive timepoints
Seroconversion rates will be assessed using a YF MN assay Seroconversion is defined as a 4-fold increase in NAb titers as compared to the prevaccination value
Time frame: 28 days after the coadministration of MMR with vYF At Month 6 and yearly from Year 1 to Year 3
Percentage of participants with seroprotection to YF virus in all investigational vaccine groups 28 days after the co-administration of vYF with measlescontaining vaccine in the MMR group and at successive timepoints
Seroprotection is defined as NAb titers ≥ 10 (1/dil) at the corresponding timepoint
Time frame: 28 days after the coadministration of MMR with vYF At Month 6 and yearly from Year 1 to Year 3
GMTs of neutralizing antibodies against YF virus in all investigational vaccine groups 28 days after the co-administration of vYF with measlescontaining vaccine in the MMR group and at successive timepoints
Antibody titers are expressed as geometric mean titers
Time frame: 28 days after the coadministration of MMR with vYF At Month 6 and yearly from Year 1 to Year 3
GMTRs of neutralizing antibodies against YF virus in all investigational vaccine groups 28 days after the co-administration of vYF with measlescontaining vaccine in the MMR group and at successive timepoints
GMTRs Day 29/Day 01, Month 6/Day 01, Year 1/Month 6, Year 2/Year 1, Year 3/Year 2
Time frame: 28 days after the coadministration of MMR with vYF At Month 6 and yearly from Year 1 to Year 3
Percentage of participants, by age group, with seroconversion to YF virus in all investigational vaccine groups before (Day 01) and after investigational vaccine administration at various timepoints
Seroconversion is defined for measles, mumps and rubella respectively in participants seronegative at baseline as an antibody titer reaching the following thresholds for seropositivity: * Anti-measles antibody concentrations ≥ 255 mIU/mL * Anti-mumps antibody concentrations ≥ 10 (AbU)/mL * Anti-rubella antibody concentrations ≥ 10 IU/mL
Time frame: Before and 28 days after the coadministration of MMR with vYF
Percentage of participants with seroprotection to MMR before and 28 days after the coadministration of MMR with vYF in the MMR group
Time frame: Before and 28 days after the coadministration of MMR with vYF
GMTs of neutralizing antibodies against MMR virus before and 28 days after the coadministration of MMR with vYF in the MMR group
Antibody titers are expressed as geometric mean titers
Time frame: Before and 28 days after the coadministration of MMR with vYF
GMTRs of neutralizing antibodies against MMR virus before and 28 days after the coadministration of MMR with vYF in the MMR group
GMTRs Day 29/Day 01
Time frame: Before and 28 days after the coadministration of MMR with vYF
Percentage of participants with seroconversion to YF virus before the booster dose administration at Y3, then 10 days and 28 days after a vYF booster dose in the booster subset
Seroconversion rates will be assessed using a YF MN assay Seroconversion is defined as a 4-fold increase in NAb titers as compared to the prevaccination value
Time frame: At Day 11 and Day 29 after booster dose
Percentage of participants with seroprotection to YF virus before the booster dose administration at Y3, then 10 days and 28 days after a vYF booster dose in the booster subset
Seroprotection is defined as NAb titers ≥ 10 (1/dil) at the corresponding timepoint
Time frame: At Day 11 and Day 29 after booster dose
GMTs of neutralizing antibodies against YF virus before the booster dose administration at Y3, then 10 days and 28 days after a vYF booster dose in the booster subset
Antibody titers are expressed as geometric mean titers
Time frame: At Day 11 and Day 29 after booster dose
GMTRs of neutralizing antibodies against YF virus before the booster dose administration at Y3, then 10 days and 28 days after a vYF booster dose in the booster subset
GMTRs Day 11/D01 and Day 29/Day 01
Time frame: At Day 11 and Day 29 after booster dose
Percentage of participants with seroconversion to YF up to Day 29 will be described depending on the FV status at baseline (YF, Dengue, Zika) by age group
YF and Zika NAbs will be measured using a qualified MN assay Quantitation of human IgG antibodies against dengue virus (DENV) nonstructural protein 1 (NS1) in human sera will be determined using a qualified ELISA assay. Seroconversion is defined as a 4-fold increase in NAb titers as compared to the prevaccination value
Time frame: Up to Day 29
Percentage of participants with seroprotection to YF up to Day 29 will be described depending on the FV status at baseline (YF, Dengue, Zika) by age group
Seroprotection is defined as NAb titers ≥ 10 (1/dil) at the corresponding timepoint
Time frame: Up to Day 29
GMTs of neutralizing antibodies against YF up to Day 29 will be described depending on the FV status at baseline (YF, Dengue, Zika) by age group
Antibody titers are expressed as geometric mean titers
Time frame: Up to Day 29
GMTRs of neutralizing antibodies against YF up to Day 29 will be described depending on the FV status at baseline (YF, Dengue, Zika) by age group
GMTRs Day 29/Day 01
Time frame: Up to Day 29
Number of participants with immediate adverse events
Immediate adverse events are any unsolicited systemic adverse events reported in the 30 minutes after vaccination
Time frame: Within 30 minutes after each vaccination
Number of participants with solicited injection site reactions
Solicited injection site reactions: * for participants \< 24 months include: injection site tenderness, injection site erythema, injection site swelling * for participants aged ≥ 2 years and \< 5 years include: injection site pain, injection site erythema and injection site swelling
Time frame: Within 7 days after each vaccination
Number of participants with solicited systemic reactions
Solicited systemic reactions: * for participants \< 24 months include: fever, vomiting, crying abnormal, drowsiness, appetite lost, irritability * for participants aged ≥ 2 years and \< 5 years include: fever, headache, fatigue and myalgia
Time frame: Within 14 days after each vaccination
Number of participants with unsolicited adverse events (AEs)
Unsolicited (spontaneously reported) AEs, not fulfilling criteria for solicited adverse reactions
Time frame: Within 28 days after each vaccination
Number of participants with medically attended adverse events (MAAEs)
MAAEs will be collected as part of the unsolicited AEs
Time frame: From Day 01 to Day 29
Number of participants with serious adverse events (SAEs) and adverse events of special interest (AESIs)
SAEs and AESIs
Time frame: From Day 01 to Month 6 and from Year 3 to Year 3 + 6 Months for the booster subset
Hematology in a subset of participants 9-24 months of age and in a subset of participants aged 2-5 years
Blood samples will be taken for the determination of hematology
Time frame: At Day 01 and at Day 05
Biochemistry in a subset of participants 9-24 months of age and in a subset of participants aged 2-5 years
Blood samples will be taken for the determination of biochemistry
Time frame: At Day 01 and at Day 05
YF vaccinal viremia in each vaccine groups (vYF, Stamaril and YF-VAX) in a subset of participants 9-24 months of age
YF vaccinal viremia will be measured by YF-specific quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay
Time frame: At Day 01 and at Day 05
Plan to share: 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
Started Jul 2025 (actual). Primary completion is estimated for Nov 2026, 16 months after the start.
Primary completion moved once since we started tracking on Sep 25, 2026: Aug 2026 → Nov 2026, on Oct 14, 2026.
Earlier changes are on the record history on ClinicalTrials.gov ↗
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
This study is active, not recruiting, as verified in Nov 2026. You cannot join it, but the record below documents what was studied.
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