We provide evidence that measurement of activity of the JAK-STAT1/2 signaling pathway in whole blood, PBMCs, or T-cell subsets, from patients with an infectious disease allows distinction between viral and bacterial infection and is informative on the strength of the adaptive cellular immune response against a viral infection and potential a complement assay to assays measuring IgG antibody responses, providing comprehensive measurement of an adaptive immune response to vaccine candidates. Here, STAT1 is linked to viral infectious disease.