There is provided a method of evaluating risk of severe outcome of an infectious disease and/or an inflammatory disease in a patient, the method comprising: determining/measuring the number of one or more immune cells selected from the group consisting of VD2 T cells, CD8 T cells, and immature neutrophils in a sample obtained from the patient, wherein the patient has an enhanced risk of severe infectious disease and/or inflammatory disease outcome when: (i) the ratio of immature neutrophils to VD2 T cell is at least 2:1, and/or (ii) the ratio of immature neutrophils to CD8 T cell is at least 0.5:1. Also disclosed are method of treating a patient with a severe infectious disease and/or inflammatory disease and kit for use in methods thereof.