The variable susceptibility of Ifnar1−/− mice to influenza-induced disease caused some confusion in the literature with many studies investigating this; however, differences in influenza strain or dose and use of either Ifnar1−/− or Stat1−/− mice as models of IFN signaling deficiency on B6, 129, CD1, or mixed mouse backgrounds make comparisons between (and even within) these studies difficult (Garcia-Sastre and others 1998; Durbin and others 2000; Price and others 2000; Mordstein and others 2008; Szretter and others 2009). The gene discussed is IFNAR1; the disease is influenza.