Efficacy of a dengue vaccine candidate (TAK-003) in healthy children and adolescents two years after vaccination

Background Takeda's dengue vaccine is under evaluation in an ongoing Phase 3 efficacy study; we present an update after 2 years. Methods 20,099 children (4-16 years old) were randomized to receive two doses of TAK-003 or placebo three months apart and are under long-term febrile surveillance to detect dengue by serotype-specific RT-PCR. (NCT02747927). Results Cumulative efficacy against dengue over ~27 months since first dose was 72.7% (95% CI: 67.1 - 77.3), which included efficacy of 67.0% (95% CI: 53.6 - 76.5) in dengue-naive and 89.2% (82.4 - 93.3) against hospitalized dengue. In the second year after vaccination, a decline in efficacy was observed [56.2% (42.3 - 66.8)] with the largest decline in 4 - 5 year-old children [24.5% (-34.2 - 57.5)]; efficacy was 60.6% (43.8 - 72.4) in 6 - 11 year and 71.2% (41.0 - 85.9) in 12 - 16 year age groups. As TAK-003 efficacy varies by serotype, changes in serotype dominance partially contributed to the efficacy differences in year by year analysis. No related serious adverse events occurred during the second year. Conclusion TAK-003 demonstrated continued benefit independent of baseline serostatus in reducing dengue with some decline in efficacy during the second year. Three-year data will be important to see if efficacy stabilizes or declines further.