EPO and herpes zoster: Specifically, we examined changes in lymphocyte count, which has been shown to decrease by treatment with tofacitinib, another JAK inhibitor19, changes in hemoglobin levels, which is expected to decrease via inhibition of erythropoietin signaling6, and the incidence of herpes zoster, as treatment with JAK inhibitors including baricitinib has been reported to increase the risk of herpes zoster in a Japanese sub-population13.