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

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.

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.

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.

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. Study registration. Netherlands Trial Registry (https://www.trialregister.nl/), NL9342.