MO224: Antibody Responses to a 3RD Booster Dose of SARS-COV-2 Vaccines in Patients with Vasculitides and Renal Involvement

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BACKGROUND AND AIMSImmunosuppressed patients are in general less likely to achieve a detectable antibody response to SARS-CoV-2 after the primary doses of vaccine administration. However, there are limited data for the effect of a third booster dose in this patient population, especially for those with vasculitides and renal involvement treated with rituximab (RTX).METHODWe retrospectively assessed the antibody responses to SARS-CoV-2 vaccination, after completion of the primary vaccine series (two doses) and after the booster third dose, in patients with vasculitides and renal involvement. IgG antibodies to the spike protein S1 subunit of SARS-CoV-2 were measured using ELISA >1 month after completion of the primary vaccination series (two doses of Pfizer or AstraZeneca vaccines) and 15–30 days after the third booster dose (Pfizer, given 3–6 months after the second dose).RESULTSWe included 20 patients with vasculitis [AAV, n = 16 (80%), IgAV, n = 4 (20%)] and renal involvement. All patients received immunosuppressives, including RTX (80%), MMF/AZA (15%), cyclophosphamide (5%), while half of patients were on glucocorticoids. The seroconversion rate after the primary two doses (Pfizer n = 8/16, Astra-Zeneca n = 1/1) was 53%, which increased to 67% after the third booster dose (Pfizer, n = 12/18). Similarly, the median antibody titers increased from 451 U/mL [interquartile range (IQR) 81–10.845] after the second dose to 1016 U/mL (ΙQR: 64–37.568) after the booster dose. Regarding patients treated with RTX, the respective response rates after the second and third dose were 58% and 62%. Seropositive patients after the third dose tended to have lower previous cumulative exposure to RTX compared with seronegative ones (4.55 versus 5.5 g, P = .62, respectively). No vaccine side effects or disease relapses were noted after the three vaccine doses.CONCLUSIONIn our patient cohort with systemic vasculitis and renal involvement treated mainly with RTX, a third booster vaccine dose increased the seropositivity rate from 53% to 67%. Nevertheless, one-third of patients did not achieve seroconversion. Whether a fourth booster dose could benefit these patients is still unknown.