The prolonged persistence of anti-viral IgM antibodies was described after different acute viral infections and live viral vaccines: the Japanese encephalitis live vaccine [83], acute hepatitis A infection [84], dengue virus infection [85], Zika virus > two years [86], yellow fever virus vaccine > 3–4 years [87], and in cerebrospinal liquid and blood of patients after West Nile virus infection [88,89,90,91] in some cases up to 8 years after infection. The gene discussed is CD40LG; the disease is viral encephalitis.