IFIH1 and COVID-19: MDA5 is activated by SARS-CoV-2 RNA in nasopharynx.412 Like RIG-I, MDA5 expression is higher in airway epithelial cells and immune cells in children than in adults, possibly explaining lower severe COVID-19 rates in children.414,415 In addition, upregulated MDA5 is observed in circulating leukocytes, PBMCs and nasopharyngeal epithelial cells from COVID-19 patients compared to healthy controls.338,423,424