This study used 3 different formulations of tetravalent CYD dengue vaccine.

The primary objective of the study was to evaluate the neutralizing antibody response after 2 doses of two different formulations of tetravalent dengue vaccine administered at Month 0 and Month 6.

The secondary objectives were:

• To evaluate the safety of the 3 formulations of tetravalent CYD dengue vaccine.
• To describe the neutralizing antibody responses to each of the 3 vaccine formulations.
• To describe vaccine viremia after the first and second dose of each of the 3 vaccine formulations in a subset of participants.

All participants provided blood samples for immunogenicity assessments, while vaccine viremia was assessed in a subset of participants in each group.

Safety was assessed in all participants as follows: solicited adverse event (AE) prelisted in the diary card were collected for 7 days after vaccination for solicited injection site reactions and 14 days for solicited systemic reactions , unsolicited AEs were collected for 28 days after vaccination, and serious adverse event (SAE) information collected throughout the study up to 6 months after vaccination.

Inclusion Criteria:

• Healthy, as determined by medical history, clinical examination, and biological safety parameters.
• Aged 18 to 45 years on the day of inclusion.
• Provision of informed consent signed by the participant or another legally acceptable representative.
• For a woman of child-bearing potential, use of an effective method of contraception or abstinence for at least 4 weeks prior to the first vaccination, and until at least 4 weeks after the last study vaccination.
• Able to attend all scheduled visits and to comply with all trial procedures.

Exclusion Criteria:

• Personal or family history of thymic pathology (thymoma), thymectomy, or myasthenia.
• For a woman of child-bearing potential, known or suspected pregnancy or positive serum/urine pregnancy test.
• Breast-feeding woman.
• Participation in another clinical trial investigating a vaccine, drug, medical device, or a medical procedure in the 4 weeks preceding the first trial vaccination.
• Planned participation in another clinical trial during the present trial period.
• Known or suspected congenital or acquired immunodeficiency, immunosuppressive therapy such as anti-cancer chemotherapy or radiation therapy within the preceding 6 months, or long-term (at least 2 weeks within the previous 3 months) systemic corticosteroids therapy (at a dose of at least 10 mg). Topical steroids were allowed.
• Known systemic hypersensitivity to any of the vaccine components or history of a life-threatening reaction to the trial vaccine or to a vaccine containing any of the same substances.
• Chronic illness at a stage that could interfere with trial conduct or completion, in the opinion of the investigator.
• Current or past alcohol abuse or drug addiction that may interfere with the participant's ability to comply with trial procedures.
• Receipt of blood or blood-derived products in the past 3 months, that might interfere with the assessment of immune response.
• Receipt of any vaccine in the 4 weeks preceding the first trial vaccination.
• Planned receipt of any vaccine in the 4 weeks following each of the trial vaccinations.
• Human Immunodeficiency Virus (HIV), hepatitis B surface antigen, or hepatitis C virus seropositivity in blood sample taken at Screening.
• Participant deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized without his/her consent.
• Clinically significant laboratory test abnormalities (as determined by the investigator) in blood sample taken at Screening.
• Previous residence in, travel or planned travel of more than 2 weeks during the study period to areas with high dengue infection endemicity.
• Reported history of flavivirus infection as reported by the participant.
• Previous vaccination against flavivirus diseases (including Japanese encephalitis, tick-borne encephalitis, and yellow fever).
• Flavivirus vaccination planned during the trial period.