The aim of the study was to evaluate a compressed dosing schedule and the immunologic effects of co-administration of a CYD dengue vaccine with a licensed flavivirus (FV) with Japanese encephalitis (JE) vaccine.

Primary Objectives:

• To describe and compare the humoral immune response to each of the 4 parental dengue virus serotypes at baseline and 28 days after each CYD dengue vaccine dose.
• To describe the persistence of the humoral immune response to each of the 4 parental dengue virus serotypes 6 after CYD dengue vaccine Dose 3, irrespective of whether or not JE vaccine had been previously administered.

Secondary Objectives:

• To describe the safety profile after each injection of CYD dengue vaccine.
• To describe the humoral immune response to each of the 4 parental dengue virus serotypes at baseline and 28 days after each CYD dengue vaccine dose when administered with or after JE virus vaccine in Groups 3 and 4.
• To describe the persistence of the humoral immune response to each of the 4 parental dengue virus serotypes at 6 months post-dose 3 in all four groups and at 12 months post-dose 3 in Groups 1 and 3 with the compressed schedule.
• To determine the level of viremia on Day (D)0, D3, D5, D7 and D14 following each CYD vaccine dose administered in Groups 1-4.
• To describe the JE humoral immune response at baseline and 28 days after each injection of CYD dengue vaccine in Groups 3 and 4.

Study participants were randomly assigned to one of the four groups to receive assigned study vaccine and were evaluated for neutralizing antibody titers; markers of cell-mediated immunity.

Inclusion Criteria:

• Aged greater than or equal to (>=)18 to less than or equal to (<=) 45 years on the day of inclusion.
• Informed consent form had been signed and dated.
• Able to attend all scheduled visits and complied with all trial procedures.
• Participant was in good health, based on medical history and physical examination.

Exclusion Criteria:

• Participant was pregnant, or lactating, or of childbearing potential (were considered of non-childbearing potential, a female had to be post- menopausal for at least 1 year, surgically sterile, or used an effective method of contraception or abstinence from at least 4 weeks prior to the first vaccination and until at least 4 weeks after the last vaccination).
• Participation in the 4 weeks preceding the first trial vaccination, or planned participation during the present trial period, in another clinical trial investigating a vaccine, drug, medical device, or medical procedure.
• Receipt or planned receipt of any vaccine, outside the study protocol in the 4 weeks preceded or followed trial vaccinations. (If influenza activity warranted vaccination of healthy young adults, influenza vaccination was encouraged and did not lead to study exclusion).
• Any history of FV vaccination, or planned FV vaccination during the trial period.
• Previous residence (greater than [>]12 months) in, or travel in the last 30 days to dengue endemic regions.
• Receipt of immune globulins, blood or blood-derived products in the 3 months prior to first vaccination or planned use during the study period.
• Known or suspected congenital or acquired immunodeficiency; or receipt of immunosuppressive therapy such as anti-cancer chemotherapy or radiation therapy within the preceded 6 months; or long-term systemic corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks within the past 3 months)
• Known systemic hypersensitivity to any of the vaccine components (including protamine sulfate), or history of a life-threatening reaction to the vaccine(s) used in the trial or to a vaccine containing any of the same substances, including dry natural latex.
• Deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized involuntarily.
• Excessive alcohol consumption or drug addiction.
• Chronic illness that, in the opinion of the Investigator, was at a stage where it might interfere with trial conduct or completion.
• Identified as an employee of the Investigator or study center, with direct involvement in the proposed study or other studies under the direction of that Investigator or study center, as well as family members (i.e., immediate, husband, wife and their children, adopted or natural) of the employee or the Investigator.
• Temporary Exclusion Criteria: Moderate or severe acute illness/infection (according to Investigator judgment) on the day of vaccination or febrile illness (temperature >= 38.0 degree Celsius [>= 100.4 degree fahrenheit]). A prospective participant was not included in the study until the condition had resolved or the febrile event had subsided. If the delay for the febrile illness exceeded the window between screening and vaccination, or if deemed necessary by the Investigator, a prospective participant might be re-screened once the fever had resolved.

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