These two patients had IgM-positive results to both JEV and DENV, however a ≥4-fold rise of anti-JEV PRNT90 titer and a ≥4-fold difference between anti-JEV PRNT90 titer and anti-DENVs titers were observed in their S2 specimen, indicating a low level of cross-reactivity in the cases of primary JEV/flavivirus infection. The gene discussed is CD40LG; the disease is Flavivirus Infections.