Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a type of systemic vasculitis characterized by autoantibody development against the neutrophil proteins leukocyte proteinase 3 (PR3)-ANCA and myeloperoxidase (MPO)-ANCA. We previously reported that newly developed AAV in Japan was influenced by seasonal variations and that AAV was less frequently observed in autumn.1.