This study was a Phase I/II, open-label trial with one treatment group; 7, healthy, flavivirus naïve children between the ages of 6 and 7 years residing in Bangkok, Thailand. Seronegative status was determined by measuring neutralizing (N) antibody titers to dengue 1-4 and JE virus (JE) using hemagglutination inhibition (HAI) (1st) and PRNT (2nd) assays. Titers <10 and <10, respectively, were considered negative. Enrolled children received two doses of tetravalent dengue vaccine at study months 0 and 6, and two doses of JE vaccine (study benefit) at study months 7 and 7.5. Enrolled children attended 20 study visits, received 4 injections, and 7 venipunctures (one additional blood sample for screening). In the acute period (1 month) following vaccination, safety was assessed using symptom diary cards and clinical and laboratory evaluations. Viremia was measured 10 days post dengue vaccination. Solicited and unsolicited adverse events were assessed for 30 days following each dengue vaccination. Serious adverse events were assessed throughout the study period. In the case of illness, investigators would complete additional clinical and virologic evaluations. Dengue vaccine immunogenicity was assessed 30 days following each dengue vaccination using the PRNT50 assay. The According to Protocol (ATP) cohort was determined by evaluating the occurrence of intermittent natural dengue infection using ELISA IgM/IgG titer ratios. A long-term follow-up of dengue vaccine recipients is described in a separate protocol (Dengue-005 protocol).