Promising efficacy of following a third dose of mRNA SARS-CoV-2 vaccination in patients treated with anti-CD20 antibody who failed 2-dose vaccination

Anti-CD20 antibodies react with CD20 expressed not only on malignant B cells but also on normal B cells. It has been reported that patients treated with anti-CD20 antibodies had an insufficient response to two-dose mRNA SARS-CoV-2 vaccination. To investigate the efficacy of a third dose in these patients, we investigated serum IgG antibody titers for S1 protein after third vaccination in 22 patients treated with anti-CD20 antibody who failed two-dose vaccination. Results showed that overall, 50% of patients seroconverted. Although no patient who received the third dose within 1 year of the last anti-CD20 antibody administration showed an increase in S1 antibody titer, 69% of patients who received the third dose more than 1 year after the last anti-CD20 antibody administration seroconverted. Our data show that a third dose of vaccination is effective in improving seroconversion rate in patients treated with anti-CD20 antibody who failed standard two-dose vaccination.