396-403
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
Authors: Kriengsak Limkittikul, Weerawan Hattasingh, Danaya Chansinghakul, Arunee Sabchareon, Wut Dulyachai, Carina Frago, T Anh Wartel, Edith Langevin, Sophia Gailhardou, Alain Bouckenooghe
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Objective: To investigate the long-term safety of a tetravalent dengue vaccine (CYD-TDV) in
children in a phase II b follow-up study in Thailand.
Methods: In the phase II 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 (<9 and ≥9 years).
Results: Of 3 997 participants receiving ≥1 injection, 80.1% were recruited to the hospital
phase [2 131 (CYD-TDV); 1 072 (control)]. Eighty-five hospitalized VCD cases were reported
in the CYD-TDV group and 46 in the control group during the four-year hospital phase [relative
risk (RR): 0.93, 95% confidence interval (CI): 0.64-1.36]. The RR over six years of follow-up
was 0.77 (95% CI: 0.57-1.05). In those aged ≥9 years, the cumulative RRs in the active phase,
hospital phase, and entire six years were 0.28 (95% CI: 0.08-0.81), 0.51 (95% CI: 0.25-1.05),
and 0.42 (95% CI: 0.24-0.75), respectively. In the overall population, there were ten severe
hospitalized VCD cases in the CYD-TDV group and five in the control group over six years (RR:
1.00, 95% CI: 0.31-3.75).
Conclusions: Over six years of follow-up, in children aged ≥9 years, CYD-TDV
administration is associated with a reduced risk of hospitalized VCD.