Seroconversion after a third COVID-19 vaccine is affected by rituximab dose but persistence is not in patients with rheumatoid arthritis

Objectives: In patients with RA treated with (ultra-)low-dose rituximab (RTX), we investigated the association of dosing and timing of RTX on seroconversion after a third coronavirus disease 2019 (COVID-19) vaccination and the persistence of humoral response after a two-dose vaccination. Material and methods: In this monocentre observational study, patients from the COVAC cohort were included in the third vaccine analysis if humoral response was obtained 2-6 weeks after a third vaccination in previous non-responders and in the persistence analysis if a follow-up humoral response was obtained before a third vaccination in previous responders. Dichotomization between positive and negative response was based on the assay cut-off. The association between the latest RTX dose before first vaccination, timing between the latest RTX dose and vaccination and response was analysed with univariable logistic regression. Results: Of the 196 patients in the cohort, 98 were included in the third vaccine analysis and 23 in the persistence analysis. Third vaccination response was 19/98 (19%) and was higher for 200 mg RTX users [5/13 (38%)] than for 500 and 1000 mg users [7/37 (19%) and 7/48 (15%), respectively]. Non-significant trends were seen for higher response with lower dosing [200 vs 1000 mg: odds ratio (OR) 3.66 (95% CI 0.93, 14.0)] and later timing [per month since infusion: OR 1.16 (95% CI 0.97, 1.35)]. Humoral response persisted in 96% (22/23) and 89% (8/9) of patients who received RTX between the two measurements. Conclusions: Repeated vaccination as late as possible after the lowest RTX dose possible seems the best vaccination strategy. A once positive humoral response after COVID-19 vaccination persists irrespective of intercurrent RTX infusion.