Acquired Immunodeficiency in ANCA Associated Vasculitis

Inclusion Criteria: To be included in the trial all participants must: * Have given written informed consent to participate * Be aged 40 years and over For patients in Group 1 only (rituximab treated): * Have a diagnosis of AAV \[granulomatosis with polyangiitis (GPA) or microscopic polyangiitis (MPA) or eosinophilic granulomatosis with polyangiitis (eGPA)\] * Have current or historical PR3/MPO ANCA positivity by ELISA or histological confirmation of AAV * Have received ≥ 2g rituximab * Have received their last dose of rituximab at least 12 months prior to enrolment * Be in stable remission with a prednisolone dose of ≤ 5mg/day For patients in Group 2 only (disease controls who have never received rituximab): * Have a diagnosis of AAV (GPA, MPA or eGPA) * Have current or historical PR3/MPO ANCA positivity by ELISA or histological confirmation of AAV * Have received cyclophosphamide (oral or IV) as initial induction therapy * Be on stable immunosuppression for the 6 months preceding screening including prednisolone ≤ 5mg/day AND either azathioprine, methotrexate or mycophenolate mofetil (at stable or tapering dose) For healthy controls: • Healthy individuals aged 40 years and over Exclusion Criteria: The presence of any of the following will preclude participant inclusion: * Age \< 40 years * History of severe allergic or anaphylactic reactions to pneumococcal vaccinations * Pneumococcal vaccination within 5 years prior to screening * Females who are pregnant, plan to become pregnant, or breast feeding * Medical, psychiatric, cognitive or other conditions that, in the investigator's opinion, compromise the patient's ability to understand the patient information, give informed consent, comply with the trial protocol, or to complete the study. * History of malignancy within the past five years or any evidence of persistent malignancy, except fully excised basal cell or squamous cell carcinomas of the skin, or cervical carcinoma in situ which has been treated or excised in a curative procedure. * Replacement immunoglobulin (IVIg) administered intravenously or subcutaneously in the 12 weeks prior to screening visit. For patients in Groups 1 and 2 only (AAV patients): * Presence of another multisystem autoimmune rheumatic disease * The prior receipt of more than 36g of cumulative cyclophosphamide ever (either IV or oral) For patients in group 1 only (rituximab group) • The receipt of any immune suppressing agent (azathioprine, methotrexate or mycophenolate mofetil) after rituximab For patients in Group 2 only (disease controls): * A relapse of AAV within the 6 months prior to screening which has necessitated an increase in prednisolone or azathioprine, methotrexate or MMF dose. * Previous rituximab therapy at any time For healthy controls: * Any history of any autoimmune condition * Any history of use of immune suppressing medication, including \> 4 weeks of oral glucocorticoids, within the 5 years prior to screening.