The primary objective of the Phase 2 study was to assess the efficacy of the CYD dengue vaccine after three injections in preventing symptomatic virologically-confirmed dengue (VCD) cases, regardless of the severity, due to any of the four serotypes in children aged 4 to 11 years at the time of inclusion.

Secondary objectives included to assess:

Vaccine efficacy against severe VCD cases

Vaccine efficacy against VCD cases following at least two injections with CYD dengue vaccine

Immune response to CYD dengue vaccine

The safety profile of CYD dengue vaccine. Safety assessments include solicited reactions within 7 or 14 days after each injection, unsolicited adverse events within 28 days after each injection, and serious adverse events during the study period.

Other objectives included:

Vaccine efficacy against VCD cases following at least one injection with CYD dengue vaccine

Vaccine efficacy against VCD cases due to each serotype

Participants with clinical signs and symptoms for VCD

Results

New England Journal of Medicine published on July 26, 2018, the results of this clinical trial.

Results: Among dengue-seronegative participants 2 to 16 years of age, the cumulative 5-year incidence of hospitalization for VCD was 3.06% among vaccine recipients and 1.87% among controls, with a hazard ratio (vaccine vs. control) through data cutoff of 1.75 (95% confidence interval [CI], 1.14 to 2.70). Among dengue-seronegative participants 9 to 16 years of age, the cumulative incidence of hospitalization for VCD was 1.57% among vaccine recipients and 1.09% among controls, with a hazard ratio of 1.41 (95% CI, 0.74 to 2.68). Similar trends toward a higher risk among seronegative vaccine recipients than among seronegative controls were also found for severe VCD. Among dengue-seropositive participants 2 to 16 years of age and those 9 to 16 years of age, the cumulative incidence of hospitalization for VCD was 0.75% and 0.38%, respectively, among vaccine recipients and 2.47% and 1.88% among controls, with hazard ratios of 0.32 (95% CI, 0.23 to 0.45) and 0.21 (95% CI, 0.14 to 0.31). The risk of severe VCD was also lower among seropositive vaccine recipients than among seropositive controls.

Conclusions: CYD-TDV protected against severe VCD and hospitalization for VCD for 5 years in persons who had exposure to dengue before vaccination, and there was evidence of a higher risk of these outcomes in vaccinated persons who had not been exposed to dengue.