Our discovery that the lack of Ifitm3 can alter the pathogenesis of RSV infection suggests IFITM3 either directly restricts RSV cell infection in vivo, or exerts a hitherto uncharacterised function controlling virus infection in vivo is novel and supports associations seen in the mouse model [43,44], in airway epithelial cultures [45] and in blood from hospitalised infants [46]. This evidence concerns the gene IFITM3 and viral infectious disease.