Given the role of eosinophils in the pathology of EGPA, biologics targeting IL-5, the major cytokine responsible for eosinophil differentiation, survival and activation [43–45], have been investigated for use in EGPA, and have shown benefit as OCS-sparing treatments [30, 46]. Here, IL5 is linked to eosinophilic granulomatosis with polyangiitis.