However, whether the association between SARS-CoV-2 vaccine and autoimmune manifestations is coincidental or causal remains to be elucidated. an increase in the development of AAV has been observed during 2021 in comparison with 2019, which could be due to the administration of SARS-CoV-2 vaccine. strong class=”kwd-title” Subject areas: Health sciences, Clinical finding, Disease Graphical abstract Open in a separate window Introduction Mass vaccination against SARS-CoV-2 has been the most effective strategy to combat against SARS-CoV-2 infection, conferring a 95% protection against COVID-19 and reducing hospitalization and mortality (Mathieu et?al., 2021). As of 10 January 2022, 90.4% of Spanish population over 12 years had received complete vaccination schedule against SARS-CoV-2, being BNT162b2 (Pfizer-BioNTech) (69.4%), mRNA-1273 (Moderna) (17.9%), the main vaccines administrated. Likewise, although to a lesser extent, AZD1222 (Oxford-AstraZeneca) (10.2%) and Ad26.CoV2.S (Janssen) (2.5%) vaccines have also been used (https://www.mscbs.gob.es/profesionales/saludPublica/ccayes/alertasActual/nCov/vacunaCovid19.htm, n.d.). The mentioned vaccines have been shown to be safe and effective, and the most prevalent short-term side effects have mostly involved injection site reaction. Severe related adverse events have been rare. However, different immune-mediated diseases, including cases of myocarditis or glomerulonephritis (GN) have been reported, antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis being one of the possible side effects caused by the mass-scale vaccination (Gargano et?al., 2021; Sekar et?al., 2021). Vasculitis is a disorder characterized by damage of mural structures of blood vessels LY2801653 dihydrochloride caused by the infiltration of mononuclear cells in vessel walls. ANCA-associated vasculitis (AAV) is characterized by the development of autoantibodies against antigens in cytoplasmic granules of neutrophils affecting predominantly to small vessels, with myeloperoxidase (MPO) LY2801653 dihydrochloride or proteinase 3 (PR3) LY2801653 dihydrochloride being the main antigens toward which these autoantibodies are directed. Although the development of ANCA after influenza vaccination has been previously reported, most of the studies that analyze the possible relationship between SARS-CoV-2 vaccination and the development of ANCA and AAV correspond to case reports (Chen et?al., 2021; Davidovic et?al., 2021; Dube et?al., 2021; Feghali et?al., 2021; Felzer et?al., 2021; Hakroush and Tampe, 2021; Okuda et?al., 2021). Likewise, the few published works that include series of patients and review the temporal association between glomerular disease and SARS-CoV-2 vaccination only include very few cases of AAV, as these studies consider the effect of the vaccine on the development of different types of glomerulonephritis, such as immunoglobulin A (IgA) LY2801653 dihydrochloride nephropathy, membranous nephropathy, minimal change disease, collapsing glomerulopathy, or lupus nephritis (Caza et?al., 2021; Fenoglio et?al., 2022; Klomjit et?al., 2021). Therefore, to our knowledge, this is the largest study that include patients who debuted with ANCA and AAV during 2021 after receiving vaccination against SARS-CoV-2 without suffering from COVID-19, in comparison with 2019, before the COVID-19 pandemic. Results A total of 35 patients presented ANCA and/or anti-GBM antibodies for the LY2801653 dihydrochloride first time during 2021, with the number during 2019 being 15. Throughout 2019 and 2021, a similar number of ANCA and/or anti-GBM antibodies determinations were carried out. Specifically, this study was performed in 1,287 patients in 2019 and 1,434 patients during 2021. Monitorization of the mentioned autoantibodies was not taken into account. Consequently, the percentage of patients who debuted with these autoantibodies in 2019 was 1.17%, whereas in 2021 this percentage increased to 2.44%, the differences observed being statistically significant (p?= 0.020) (Figure?1). Mean age of the patients included was 65.8 and GTF2F2 63.1 years in 2019 and 2021, respectively. No statistically significant difference on gender was observed. In 2019, the most frequent ANCA was anti-MPO, being present in 80.0% of the patients. However, in 2021, an.