Phase 3 Randomized, Modified Double-blind, Active-controlled Safety Study on vYF in Adults

Inclusion Criteria:

• Aged from 18 years to 60 years on the day of inclusion

• Participants who are healthy as determined by medical evaluation including medicalhistory and physical examination

• A female participant is eligible to participate if she is not pregnant orbreastfeeding and one of the following conditions applies:

• Is of non-childbearing potential. To be considered of non-childbearingpotential, a female must be post-menopausal for at least 1 year, or surgicallysterile.

OR

-Is of childbearing potential and agrees to use an effective contraceptive method or abstinence from at least 4 weeks prior to study intervention administration until at least 12 weeks after study intervention administration.

• A female participant of childbearing potential must have a negative highly sensitivepregnancy test (urine or serum as required by local regulation) before any dose ofstudy intervention on D01 and will be repeated on D29 to confirm the participant isstill not pregnant within the 28 days of vaccine administration

• Able to attend all scheduled visits and to comply with all study procedures Informedconsent

• Informed consent form has been signed and dated

Exclusion Criteria:

• Known or suspected congenital or acquired immunodeficiency; or receipt ofimmunosuppressive 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 3months)

• Known history of laboratory evidence of HIV infection

• Known history of hepatitis B or hepatitis C seropositivity

• Known history of flavivirus (FV) infection

• Known systemic hypersensitivity to any of the study intervention components, orhistory of a life-threatening reaction to the vaccine used in the study or to avaccine containing any of the same substances

• Personal or family history of thymic pathology (thymoma, thymectomy, or myasthenia)

• Chronic illness that, in the opinion of the investigator, is at a stage where itmight interfere with trial conduct or completion , including malignancy, such asleukemia or lymphoma

• Moderate or severe acute illness/infection (according to Investigator judgment) onthe day of vaccination or febrile illness (temperature ≥ 38°C [or ≥ 100.4°F]). Aprospective participant should not be included in the study until the condition hasresolved or the febrile event has subsided.

• Alcohol, prescription drug, or substance abuse that, in the opinion of theInvestigator, might interfere with the study conduct or completion

• Receipt of any vaccine in the 4 weeks preceding the study vaccination or plannedreceipt of any vaccine in the 4 weeks following the study vaccination (prior toVisit 2 on D29), except for influenza vaccination, which may be received at least 2weeks before study vaccine. This exception includes pandemic influenza vaccinesincluding monovalent pandemic influenza vaccines.

• Previous vaccination against a FV disease at any time including yellow fever (YF)with an investigational or marketed vaccine

• Receipt of immune globulins, blood or blood-derived products in the past 6 months

• Administration of any anti-viral within 2 months preceding the vaccination and up tothe 6 weeks following the vaccination

• Participation at the time of study enrollment (or in the 4 weeks preceding the studyvaccination) or planned participation during the course of the study in anotherclinical study investigating a vaccine, drug, medical device, or medical procedure

• Deprived of freedom by an administrative or court order, or in an emergency setting,or hospitalized involuntarily

• Identified as an Investigator or employee of the Investigator or study center withdirect involvement in the proposed study, or identified as an immediate familymember (ie, parent, spouse, natural or adopted child) of the Investigator oremployee with direct involvement in the proposed study

• Planned travel in a YF endemic country within 6 months of investigational vaccineadministration