Since interferons (IFNs) induce the overexpression of several antiviral agents, including 2′,5′-oligoadenylate synthetase (OAS1 to OAS3) and protein kinase R (PKR) [81,82], which inhibit viral replication in infected cells [78], an elevated expression of OAS1, OAS2, and PKR can be considered a hallmark of viral infection and IFN stimulation. This evidence concerns the gene IFNA1 and viral infectious disease.