Furthermore, individuals with previous infections or immunizations by flavivirus may show the “antigenic original sin” phenomenon, i.e. they can present a specific antibody response to the virus which is responsible for the previous infection rather than to the current one.74 A commercial ELISA test that uses the NS1 antigen of ZIKV shows good performance, including in terms of specificity.75 IgG seroconversion occurs, on average, 9 days after the onset of symptoms, whereas the IgM may appear 4–5 days after the onset.41 This evidence concerns the gene CD40LG and infection.