Long-term safety follow-up of children from a randomized—controlled phase II b proof—of—concept efficacy study of the live, attenuated, tetravalent dengue vaccine (CYD—TDV) in Thailand

Objective: To investigate the long-term safety of a tetravalent dengue vaccine (CYD-TDV) in children in a phase Π b follow-up study in Thailand. Methods: In the phase Π b study, children aged 4-11 years were randomized (2:1) to receive three injections of CYD-TDV or serve as control at 6-month intervals, with 25 months’ active follow-up (active phase). This study was an additional four-year passive surveillance for hospitalized virologically-confirmed dengue (VCD; hospital phase). Cases of hospitalized VCD, severe hospitalized VCD, vaccine-related serious adverse events, and deaths were reported for the total population, with post-hoc analyses by enrollment age (