In mice, higher IFN-γ and IgG2b responses are associated with induction of YF-17D nAbs.38 In humans, high frequency of virus-specific CD4+ IFN-γ+ T cells at early time points is associated with a strong nAb response to YF-17D vaccination.39 Levels of IFN-γ, IL-12, and IFN-α are also found to be higher in dengue patients with mild fever compared to those with more severe disease,40–42 indicating that a Th1 cytokine environment might also be related to protection. This evidence concerns the gene IFNG and dengue disease.