Abstract Objective: To evaluate inactivated CoronaVac prime vaccination, antibody decay, booster dose, and safety in ANCA-Associated Vasculitis (AAV) patients. Methods: Fifty-three AAV patients and 106 Controls (CG) received CoronaVac on days: D0 (first dose), D28(second dose), and D210 (booster dose, 32 AAV: 32 CG). The primary outcome was immunogenicity after the second vaccine dose (day 69) assessed by Seroconversion Rates (SC) of anti-SARS-CoV-2 S1/S2 IgG and Neutralizing Antibodies (NAb). Secondary outcomes were safety, immunogenicity (D28/D240), 6-months antibody decay (D210) and the booster dose response (D240). Results: At D69 SC (65.1% vs. 96.8%, p = 0.0001), GMT (21.3 UA/mL vs. 67.7 UA/mL, p < 0.001) and NAb- positivity (53.7% vs. 80.6%, p = 0.001) were moderate but lower in naïve-AAV patients than CG. Patients without SC used more often IS (93.3% vs. 53.3%, p = 0.015), mycophenolate mofetil (20% vs. 0%, p = 0.037) and prednisone (60.0% vs. 28.6%, p = 0.057) than seroconverted. NAb negativity in AAV patients was associated with prednisone treatment (57.9% vs. 18.2%, p = 0.015) and IS (84.2% vs. 55.0%, p = 0.046). Logistic regression analysis models showed that only prednisone was associated with lower seroconversion (OR = 0.2, 0,95% CI 0.05–0.86, p = 0.030) and with lower NAb positivity (OR = 0.2, 0,95% CI 0.05–0.88, p = 0.034). After six months (D69–D210) a decrease in IgG positivity occurred in 32 AAV patients (15.7%, p = 0.074) and 32 CG (18.7%, p = 0.041). For the NAb positivity, the 6-month decrease was not significant (p = 0.114) whereas a major reduction occurred for CG (p < 0.001). A booster dose (D240) resulted in an increment in IgG-positivity (21.9%, p = 0.023) and NAb-positivity (34.4%, p = 0.006) in AAV patients. No moderate/severe adverse events attributable to the vaccine were observed. Conclusion: This study provides novel data on the excellent safety and moderate immunogenicity of CoronaVac in AAV patients. A six-month mild antibody waning was observed with a good response to the booster dose, although levels remained lower than CG (CoronavRheum-NCT04754698). Objective vaccination ANCAAssociated ANCA Associated (AAV Methods Fiftythree Fifty three 10 (CG days D first , dose) D28second Dsecond D28 D21 3 . CG) day 69 (SC antiSARSCoV2 antiSARSCoV anti SARS CoV 2 anti-SARS-CoV- S1S2 SS S1 S2 S S1/S NAb. (NAb) D28/D240, D28D240 DD D28/D240 D240 (D28/D240) 6months 6 (D210 D240. Results D6 65.1% 651 65 1 (65.1 vs 968 96 8 96.8% 0.0001, 00001 0.0001 0 0001 0.0001) 21.3 213 21 (21. UAmL UA mL 677 67 7 67. 0.001 001 53.7% 537 53 (53.7 806 80 80.6% naïveAAV naïve 93.3% 933 93 (93.3 533 53.3% 0.015, 0015 0.015 015 20% 20 (20 0% 0.037 0037 037 60.0% 600 60 (60.0 286 28 28.6% 0.057 0057 057 seroconverted 57.9% 579 57 9 (57.9 182 18 18.2% 84.2% 842 84 (84.2 550 55 55.0% 0.046. 0046 0.046 046 0.046) OR 02 0.2 095 95 0,95 005086 05 86 0.05–0.86 0.030 0030 030 005088 88 0.05–0.88 0.034. 0034 0.034 034 0.034) D69–D210 D69D210 (D69–D210 15.7%, 157 15 (15.7% 0.074 0074 074 18.7%, 187 (18.7% 0.041. 0041 0.041 041 0.041) 6month month 0.114 0114 114 0.001. (D240 IgGpositivity 21.9%, 219 (21.9% 0.023 0023 023 NAbpositivity 34.4%, 344 34 4 (34.4% 0.006 0006 006 moderatesevere severe Conclusion sixmonth CoronavRheumNCT04754698. CoronavRheumNCT04754698 CoronavRheumNCT CoronavRheum NCT04754698 NCT (CoronavRheum-NCT04754698) D2 anti-SARS-CoV S1S (NAb D28D24 D28/D24 D24 (D28/D240 (D21 65.1 (65. 96.8 0000 0.000 000 21. (21 0.00 00 53.7 5 (53. 80.6 93.3 (93. 53.3 0.01 01 (2 0.03 003 03 60.0 (60. 28.6 0.05 005 57.9 (57. 18.2 84.2 (84. 55.0 004 0.04 04 0. 09 0,9 00508 0.05–0.8 D69–D21 D69D21 (D69–D21 15.7% (15.7 0.07 007 07 18.7% (18.7 0.11 011 11 (D24 21.9% (21.9 0.02 002 34.4% (34.4 CoronavRheumNCT0475469 NCT0475469 (CoronavRheum-NCT04754698 D28D2 D28/D2 (D28/D24 (D2 65. (65 96. 0.0 53. (53 80. 93. (93 ( 60. (60 28. 57. (57 18. 84. (84 55. 0, 0050 0.05–0. D69–D2 D69D2 (D69–D2 15.7 (15. 18.7 (18. 0.1 21.9 34.4 (34. CoronavRheumNCT047546 NCT047546 (CoronavRheum-NCT0475469 D28D D28/D (D28/D2 (D (6 (5 (9 (8 0.05–0 D69–D D69D (D69–D 15. (15 (18 34. (34 CoronavRheumNCT04754 NCT04754 (CoronavRheum-NCT047546 (D28/D 0.05– (1 (3 CoronavRheumNCT0475 NCT0475 (CoronavRheum-NCT04754 CoronavRheumNCT047 NCT047 (CoronavRheum-NCT0475 CoronavRheumNCT04 NCT04 (CoronavRheum-NCT047 CoronavRheumNCT0 NCT0 (CoronavRheum-NCT04 (CoronavRheum-NCT0 (CoronavRheum-NCT