Results
A total of 126 participants received study vaccination at month 0 of the study, of whom 113 completed the five year follow-up. The baseline characteristics of the participants are summarised elsewhere [11].
There were no vaccine-related SAEs reported during the five year follow-up period in either study group. Only two SAEs were reported; both occurred during the fifth year of follow up in the TDV–TDV–TDV group. The first was a hospitalisation for myofascial pain syndrome in a 19 year old female participant, and the second a dengue episode in a 10 year old boy who was hospitalised with fever, abdominal pain, and vomiting. The hospitalised boy had virologically-confirmed dengue (serotype 1), but did not have severe dengue according to the World Health Organization 2009 classification (i.e. no sign of shock, haemorrhage, plasma leakage, or thrombocytopenia) and recovered four days after fever onset and discharged two days later (6 days after fever onset). Four women became pregnant during follow up; none of these pregnancies were exposed to vaccination. There were no complications with the pregnancies and the women delivered healthy babies.
During the first four years of follow up, 53 febrile episodes (suspected dengue disease) were reported by 34 participants (20 in the TDV–TDV–TDV group and 14 in the TyVi–TDV–TDV group), most of whom (n = 28) were children aged 2–11 years. Among the suspected dengue disease cases in the first four years (three in the TDV–TDV–TDV group and three in the TyVi–TDV–TDV group), six were laboratory confirmed and of these, five were virologically confirmed ( Table 1). In the case where dengue was laboratory confirmed but not virologically confirmed, the subject was positive for anti-dengue IgG and IgM but negative for RT-PCR and NS1 Ag. During the fifth year of follow-up, one additional dengue case (virologically confirmed) was reported in a boy in the 2–5 year old group ( Table 1). Overall, of the seven dengue cases that occurred during this study, four subjects were dengue seropositive and three subjects were seronegative at baseline (prior to vaccination).