Background: Patients with ANCA associated vasculitis (AAV) require immunosuppressive therapy for disease control and prevention of relapse and may therefore be at risk for a severe disease course if infected by SARS-CoV-2. The disease itself and its consequences, for example kidney damage, may also increase the risk for a severe COVID-19 infection. The objectives of this study was to analyse the outcome of COVID-19 in a large cohort of well characterized AAV patients regarding incidence and risk factors for development of severe infection. Methods: Data were retrieved from March 2020 to May 2021 from the medical records of living patients from the AAV cohorts in Stockholm and Uppsala (n=310). Extracted data includes age, gender, ongoing immunosuppressive therapy, kidney involvement (ever), lung involvement (ever) and estimated GFR (eGFR). COVID-19 was confirmed either by a positive PCR test or by serology. Severe COVID-19 was defined as need of non-invasive ventilation, ICU care and/or death. Results: The cohort comprised 232 patients with GPA, 56 with MPA and 22 with EGPA. 95% were ANCA positive (ever), the ANCA negative patients found mainly among the EGPA patients. 49% of the patients were female. During the study period 29 patients (9%) were diagnosed with COVID-19. The median age in the COVID-19 group was 60 (40-72) years, in the non-COVID group 68 (55-77) years (p=0.02). However, patients with severe COVID infection were older (p=0.07). Four deaths were related to COVID-19. Fifteen patients (52%) were on prednisolone treatment in the COVID-19 group and 130 (46%) in the non-COVID group, with significantly higher doses in the COVID-19 patients (p < 0.01). Concerning DMARD treatment, 65% were on (any) DMARD in both groups. However, induction therapy with either cyclophosphamide (CYC) and/or rituximab (RTX) and corticosteroids was more prevalent in the COVID-19 group, with 14% on induction in the COVID-group compared to 2.5% in the non-COVID group (p<0.01). Of the 29 COVID-19 cases, 9 (31%) had severe infection. Significant risk factors for severe COVID-19 was older age, impaired kidney function, higher steroid dose and ongoing induction therapy with cyclophosphamide (borderline risk for induction with CYC and /or RTX). RTX maintenance therapy was not associated with poorer disease outcome. See Table. Conclusions: Patients with AAV were at risk for a more severe COVID-19 disease course. This risk is driven by known risk factors such as older age, but also of consequences of vasculitis i.e. impaired kidney function, and by treatment related factors. Higher steroid dose and ongoing induction therapy, reflecting higher disease activity, were significant risk factors in this group. More reassuring was that maintenance therapy with RTX was not associated with a severe disease course. The findings stress the need for continued shielding and prompt and effective vaccination in AAV patients. Disclosures: None Table 1. Characteristics comparing non-severe and severe COVID-19 infection Subjects characteristics Non-severe COVID-19 Severe COVID-19 p-value Number of patients (%) 20 (69) 9 (31) Age (median, IQR) 51 (35.5-64.5) 69 (55.5-75.0) 0.02 Gender (F/M, %) 10/10(50/50) 4/5 (45/55) ns Diagnosis GPA/MPA/EGPA 16/3/1 6/2/1 ns ANCA: None/PR3/MPO/both 2/15/3/0 2/5/2/0 ns Lung involvement n (%) 13 (65) 6/9 (67) ns Renal involvement n (%) 11(55) 6/9 (67) ns eGFR (mL/min/1.7) 80.5(61.5-89.0) 53.0 (28.5-67.5) 0.01 Treatment Number on prednisolone 8(40) 7 (78) ns Prednisolone dose, mg/day (median, IQR) 5.0 (2.5-7.5) 7.5 (5.0-50.0) 0.02 DMARD (n, %) 12 (60) 7 (78) ns Induction therapy (rituximab and/or Cyclophosphamide) (n, %) 1 (5) 3 (33) 0.08 Cyclophosphamide induction (n, %) 0 2 (22) 0.05 Rituximab maintenance 7 (35) 1 (11) ns