IFNB1 and viral infectious disease: Combining smFISH for IFIT1 and IFNB1 can reveal heterogeneity in host cell responses and allow identification of at least three quantitatively and qualitatively distinct host responses to viral infection: (1) no antiviral response activation (IFIT1−/IFNB1−), (2) activation of IFIT1 expression only (IFIT1+/IFNB1−) and (3) activation of both IFIT1 and IFNB1 (IFIT1+/IFNB1+).