Inclusion Criteria:  Age ≥ 18 years old. Diagnosis of SEA by a health care provider History of an absolute eosinophil count ≥ 300/mm^3 Prescription for mepolizumab provided during course of routine clinical care but mepolizumab not yet started  Exclusion Criteria:  Age < 18 years old. Pregnancy. Currently using or have used within 3 months of the initial baseline visit any biologic or immunomodulatory therapy with the exception of #3. Currently using or any prior use of rituximab. History of upper/lower respiratory tract infection or asthma exacerbation within the previous four weeks of the first baseline visit. Any prior history of malignancy, autoimmune disease, or immune deficiency. Any other significant medical issue as determined by the principal investigator.