A Study of 2 Doses of Tetravalent Dengue Vaccine (TDV) in Infants and Toddlers

A Randomized, Age-Descending, Double-Blind, Placebo-Controlled, Phase 3 Trial to Evaluate the Safety and Immunogenicity of 2 Doses of a Subcutaneous Dengue Tetravalent Vaccine (Live, Attenuated) (TDV) Administered Within the Routine Vaccination Schedule of Pediatric Participants ≥6 Months to <21 Months of Age

Dengue fever is caused by an infection with the dengue virus. Vaccination with Dengue Tetravalent Vaccine (TDV) can help prevent dengue fever. The purpose of this study is to collect information of vaccination with TDV when given to children younger than 2 years. The main aims of this study are to learn how safe the vaccine is and how well it works to activate a young child's immune system (this is called immunogenicity). Children between the age of 6 and 21 months will receive two vaccinations with either TDV or placebo 3 months apart. Blood samples will be taken before and after the vaccination as well as throughout the study. These are necessary to check how well the vaccine works to activate the immune system. During the study, participants will visit their study clinic 8 times for vaccinations, blood draws and health checks.

Inclusion Criteria

Participant eligibility is determined according to the following criteria:

1. Participant is aged >=6 to <21 months at the time of entry into the trial.
2. Participant is male or female.
3. Participant is in good health at the time of entry into the trial as determined by medical history, physical examination (including vital signs), and the clinical judgment of the investigator.
4. Participant's legally acceptable representative (LAR) has signed and dated a written informed consent form (ICF) and any required privacy authorization prior to the initiation of any trial procedure, and after the nature of the trial has been explained according to local regulatory requirements.
5. The participant and participant's LAR can comply with trial procedures and can be available for the duration of follow-up, according to the LAR.

Exclusion Criteria

Any participant who meets any of the following criteria will not qualify for randomization:

1. Participant has contraindication(s), warning(s) and/or precaution(s) applicable to vaccination with TDV as specified in the investigator's brochure (IB)and/or the approved product label (as applicable) in the participating country.

2. Participant has a known hypersensitivity or allergy to any of the investigational medicinal product (IMP) components (including excipients).

3. Participant has behavioral or cognitive impairment or psychiatric disease that, in the opinion of the investigator, may interfere with the participant's ability to participate in the trial.

4. Participant has a history of progressive or severe neurologic disorder, seizure disorder or neuro-inflammatory disease (example, Guillain-Barré syndrome).

5. Participant has an illness, or history of any illness that, in the opinion of the investigator, might interfere with the results of the trial or pose additional risk to the participant due to involvement in this trial.

6. Participant has a known or suspected impairment/alteration of immune function, including:

   1. Chronic administration of oral and/or parenteral steroids at doses considered sufficiently immunosuppressive (example, >=2 mg/kg [milligrams per kilograms] body weight/day prednisone [or equivalent] for 14 consecutive days, or, >=20 milligram per day [mg/day] prednisone [or equivalent] for >=14 consecutive days) within 60 days prior to Day 1 month 0 (M0) (note: use of corticosteroids by inhaled, intranasal, intraarticular, bursal, tendon injection, or topical routes is allowed).
   2. Receipt of blood, immunoglobulins, blood products, and/or plasma derivatives within the 3 months prior to Day 1 (M0).
   3. Receipt of immunostimulants within 60 days prior to Day 1 (M0).
   4. Immunosuppressive therapy such as anti-cancer chemotherapy or radiation therapy within 6 months prior to Day 1 (M0).
   5. HIV infection or HIV-related disease.
   6. Hepatitis B virus infection.
   7. Hepatitis C virus infection.
   8. Genetic immunodeficiency.

7. Participant has known or suspected abnormalities of splenic or thymic function.

8. Participant has a known bleeding diathesis, or any condition/medication that may be associated with a prolonged bleeding time.

9. Participant has a serious chronic or progressive disease deemed to be preclusive to trial entry, that is., not medically stable according to the judgment of the investigator.

10. Participant has previously received a vaccination against dengue virus (investigational or licensed).

11. Participant has a clinically significant active infection (as assessed by the investigator) or body temperature greater than (>) 38.0 degrees Celsius (°C) (>100.4 degrees Fahrenheit [°F]) within 3 days of intended IMP administration on Day 1 (M0).

12. Participant has used antipyretics and/or analgesic medications within 24 hours prior to vaccination. The reason for their use (prophylaxis vs treatment) must be documented. Trial entry must be delayed to allow for a full 24 hours to have passed since last use of antipyretics and/or analgesic medications.

13. Participant has received any of the following:

    1. A licensed vaccine within 14 days (for inactivated vaccines) or 28 days (for live vaccines) prior to IMP administration on Day 1 (M0). This includes co-administration with routine vaccines.
    2. A coronavirus vaccine within 14 days prior to IMP administration on Day 1 (M0).
    3. A vaccine authorized for emergency use within 28 days prior to IMP administration on Day 1 (M0).

14. Participant is scheduled to receive any other vaccine within 28 days after IMP administration on Day 1 (M0).

15. Participant is participating in any clinical trial with another investigational product 30 days prior to Day 1 (M0) or plans to participate in another clinical trial at any time during the conduct of this trial.

16. Participant has taken part in any clinical trial of a dengue or other flavivirus (example, West Nile virus) candidate vaccine, except if it is known that the participant received placebo in the trial(s).

17. A first degree relative is involved in the conduct of this trial.