This is in line with previous reports indicating that IgM responses against flaviviruses are more specific than IgG,19 although cross-reactivity has also been described.7, 37 However, IgM antibodies are often produced only in low amounts, especially in secondary flavivirus infections or after a vaccination and are shortlived,14, 38 hence IgG measurements become necessary. This evidence concerns the gene CD40LG and Flavivirus Infections.