Cross-reactivity between SARS-CoV-2 spike (S) protein and dengue envelope protein is indicated in pre-COVID-19 pandemic serum from flavivirus infection; 20% of 19 confirmed Brazilian Zika infection [18] and 22% of 70 dengue IgG positive travelers from Israel and Italy [19] show positive IgM and/or IgG reactivity in SARS-CoV-2 S RBD rapid tests and/or semi-quantitative ELISA. The gene discussed is CD40LG; the disease is dengue disease.