STAT1 and viral infectious disease: We describe development, as well as evaluation on samples from published preclinical and clinical studies, of an mRNA-based test to quantify the immune response to a viral infection, based on measuring activity of the JAK-STAT1/2 and JAK-STAT3 signal transduction pathways in a whole blood or Peripheral Blood Mononuclear Cell (PBMC) sample, or in separate immune cell types.