JAK1 and rheumatoid arthritis: In pooled analyses of RA clinical studies, HZ IRs (events per 100 patient‐years) were: 4.4 and 4.2 with tofacitinib 5 and 10 mg BID, respectively, vs 1.5 with placebo32; 2.7 and 4.3 with baricitinib 2‐ and 4 mg QD, respectively, vs 1.0 with placebo.33 HZ has also been reported in phase 3 RA studies of upadacitinib and filgotinib.17, 18 As such, the occurrence of HZ is likely a “class effect” of inhibiting at least JAK1,34 although viral reactivation could also be dependent on the overall impact of JAK inhibition.