The purpose of this study is to assess the humoral immune responses to three different dose schedules of Takeda's Tetravalent Dengue Vaccine Candidate (TDV) administered subcutaneously in healthy participants between 2 and <18 years of age living in dengue endemic countries.

The vaccine tested in this study is Takeda's Tetravalent Dengue Vaccine Candidate (TDV) which was administered in 3 different dosing schedules to participants aged from 2 to 17 years resident in dengue endemic countries. This study looked at the titers of antibodies to dengue fever elicited in people who received TDV.

The study randomized 1800 healthy participants. Participants were randomly assigned to one of the four treatment groups in a 1:2:5:1 ratio-which remained undisclosed to the participant and study doctor during the study (unless there was an urgent medical need):

• Group 1 - TDV 0.5 mL subcutaneous (SC) injection Days 1 and 91
• Group 2 - TDV 0.5 mL SC injection Day 1
• Group 3 - TDV 0.5 mL SC injection Days 1 and 365
• Group 4 - Placebo (dummy SC) - this is a liquid that looks like the study drug but has no active ingredient

A total of 600 participants were planned to be randomly included in immunogenicity analyses (approximately 100 participants planned in each of Group 1 and Group 4, and 200 participants planned in each of Group 2 and Group 3).

In order to keep the treatment arms undisclosed to the participant and the doctor, participants received a placebo injection at any study visit where TDV was not being administered (Days 1 and/or 91 and/or 365).

Participants were asked to record any symptoms that may be related to the vaccine or the injection site in a diary card for 28 days after each vaccination.

This multi-center trial was conducted in Asia and Latin America. Participants were followed for 48 months with 10 protocol-scheduled visits for participants included in the planned immunogenicity subset of approximately 600 subjects and 7 protocol-scheduled visits for subjects not included in the immunogenicity subset.

Inclusion Criteria:

1. Is aged 2 to <18 years, at the time of enrolment.
2. Is in good health at the time of entry into the trial as determined by medical history, physical examination (including vital signs), and clinical judgment of the investigator.
3. The participant or, when applicable, the participant's legally acceptable representative signs and dates a written, informed consent form (and assent form, where required) and any required privacy authorization prior to the initiation of any trial procedures, after the nature of the trial has been explained according to local regulatory requirements.
4. Can comply with trial procedures and are available for the duration of follow-up.

Exclusion Criteria:

1. Febrile illness (temperature ≥ 38°C or 100.4°F) or moderate or severe acute illness or infection at the time of enrolment. Trial entry should be delayed until the illness has improved.
2. Individuals with history or any illness that, in the opinion of the investigator, might interfere with the results of the trial or pose additional risk to the participants due to participation in the trial, including but not limited to: a. Known hypersensitivity or allergy to any of the vaccine components; b. Female participants who are pregnant or breastfeeding; c. Individuals with any serious chronic or progressive disease according to judgment of the investigator (e.g. neoplasm, insulin-dependent diabetes, cardiac, renal or hepatic disease, neurologic or seizure disorder or Guillain-Barré syndrome); d. Known or suspected impairment/alteration of immune function, including: i. Chronic use of oral steroids (Equivalent to 20 mg/day prednisone ≥ 12 weeks / ≥ 2 mg/kg body weight / day prednisone ≥ 2 weeks) within 60 days prior to Day 1 (use of inhaled, intranasal, or topical corticosteroids is allowed); ii. Receipt of parenteral steroids (Equivalent to 20 mg/day prednisone ≥ 12 weeks / ≥ 2 mg/kg body weight / day prednisone ≥ 2 weeks) within 60 days prior to Day 1; iii. Administration of immunoglobulins and/or any blood products within the three months preceding the first administration of the investigational vaccine or planned administration during the trial; iv. Receipt of immunostimulants within 60 days prior to Day 1; v. Immunosuppressive therapy such as anti-cancer chemotherapy or radiation therapy within 6 months preceding (first) vaccination; vi. Human immunodeficiency virus (HIV) infection or HIV-related disease; vii. Genetic immunodeficiency.
3. Individuals who received any other vaccines within 14 days (for inactivated vaccines) or 28 days (for live vaccines) prior to enrollment in this trial or who are planning to receive any vaccine within 28 days of investigational vaccine administration.
4. Individuals participating in any clinical trial with another investigational product 30 days prior to first trial visit or intent to participate in another clinical trial at any time during the conduct of this trial.
5. Individuals who are first degree relatives of individuals involved in trial conduct.
6. If female of childbearing potential, sexually active, and has not used any of the "acceptable contraceptive methods" for at least 2 months prior to trial entry: a. Of childbearing potential is defined as status post onset of menarche and not meeting any of the following conditions: menopausal (for at least 2 years), bilateral tubal ligation (at least 1 year previously), bilateral oophorectomy (at least 1 year previously) or hysterectomy; b. Acceptable birth control methods are defined as one or more of the following: i. Hormonal contraceptive (such as oral, injection, transdermal patch, implant, cervical ring); ii. Barrier (condom with spermicide or diaphragm with spermicide) each and every time during intercourse; iii. Intrauterine device (IUD); iv. Monogamous relationship with vasectomized partner. Partner must have been vasectomized for at least six months prior to the participants' trial entry.
7. If female of childbearing potential, sexually active and refuses to use an "acceptable contraceptive method" through to 6 weeks after the last dose of investigational vaccine.
8. Individuals who participated in a previous dengue vaccine trial.

Takeda makes patient/subject-level, de-identified data sets and associated documents available for all interventional studies after applicable marketing approvals and commercial availability have been received (or program is completely terminated), an opportunity for the primary publication of the research and final report development has been allowed, and other criteria have been met as set forth in Takeda's Data Sharing Policy (see www.TakedaClinicalTrials.com for details). To obtain access, researchers must submit a legitimate academic research proposal for adjudication by an independent review panel, who will review the scientific merit of the research and the requestor's qualifications and conflict of interest that can result in potential bias. Once approved, qualified researchers who sign a data sharing agreement are provided access to these data in a secure research environment.