IRF7 and COVID-19: Furthermore, in mouse models, the early phase of SARS-CoV-2 infection causes an upregulation of the Tlr7, Irf7 and IFN-I pathways in the lungs, whereas Tlr7 and Irf7-deficient mice show increased COVID-19 severity caused by deficient IFN-I and -III activation (42, 43).