Long-Term Safety and Antibody Persistence of TDV and the Impact of a Booster Dose

The purpose of this study is to describe antibody persistence for each of the 4 dengue serotypes for up to 63 months after the first vaccination in the primary vaccination series for participants from parent trial DEN-315 (NCT03341637) (Mexico) and for up to 36 months after the first vaccination in the primary vaccination series for participants from parent trial DEN-304 (NCT03423173) (United States \[US\]) and to describe the impact of a tetravalent dengue vaccine (TDV) booster dose vs placebo on antibody response for each of the 4 dengue serotypes at 1 month and 6 months post administration of the TDV booster or placebo.

The vaccine tested in this study is Takeda's Dengue Tetravalent Vaccine (Live, Attenuated) (TDV). This study will look at the long-term antibody persistence and safety of Takeda's TDV in healthy adolescents and adults and will assess the impact of a booster dose. The study has enrolled 365 healthy participants. Participants who previously received TDV in two parent trials (DEN-304 \[NCT03423173\] and DEN-315 \[NCT03341637\]), will be invited to participate in this follow-up trial. Participants will be assessed for antibody persistence and safety from Baseline (Month 0) through Month 15 (for participants from parent trial DEN-304 \[US\]) or Month 42 (for participants from parent trial DEN-315 \[Mexico\]). At Month 15 (for participants from parent trial DEN-304 \[US\]) or at Month 42 (for participants from parent trial DEN-315 \[Mexico\]), eligible participants will be randomized in 1:1 ratio to one of two trial groups to receive TDV or placebo: A. Group 1- TDV 0.5 mL subcutaneous (SC) injection at Month 15 for participants from parent trial DEN-304 (US) or at Month 42 for participants from parent trial DEN-315 (Mexico\]). B. Group 2- Takeda's tetravalent dengue placebo (dummy SC injection - this is a liquid that looks like the study drug but has no active ingredient), 0.5 mL, subcutaneous injection at Month 15 for participants from parent trial DEN-304 (US) or at Month 42 for participants from parent trial DEN-315 (Mexico). This multi-centre trial will be conducted in US and Mexico. The overall time to participate in this study is up to 21 months for parent trial DEN-304 (US) and up to 48 months for parent trial DEN-315 (Mexico). Participants from parent trial DEN-304 (US) and participants from parent trial DEN-315 (Mexico) will come for 5 visits to the clinic which includes a final visit (Visit 5) 6 months after the booster dose for a follow-up assessment.