JAK inhibitors targeting JAK1 and JAK3 exhibit an increased risk of herpes zoster reactivation.5 Targeting of JAK1 and JAK3 affects the function of various cytokines involved in antiviral responses such as type I interferons (IFNs), IL-2, IL-15, IL-21, and IFN-y. This evidence concerns the gene JAK3 and herpes zoster.