Humoral responses after COVID-19 vaccination in anti-CD20-treated lymphoma patients. (A) Seroconversion rates after the first and second COVID-19 vaccination (post V1: n = 57, post V2: n = 76). The median time from the first and second vaccination to serology testing was 15 days (IQR: 14–17 days) and 16 days (IQR: 14–24.2 days), respectively. The anti-SARS-Cov-2-S1 antibody response rate after the second vaccination was significantly higher than after the first vaccination (V2 vs V1: 41% [31/76] vs 9% [5/57], McNemar test P < .001). A semiquantitative index of <1 was classified as negative, and a value of ≥1 was classified as positive. All patients with an available sample prior to vaccination (n = 70, median sample collection prior to first vaccination: 254 days, IQR: 17–448 days) were tested negatively for anti-SARS-CoV-2-S1 and anti-SARS-CoV-2-N antibodies. (B) Seroconversion rates after the first and second COVID-19 vaccination according to the interval between the last anti-CD20 treatment and first COVID-19 vaccination (<3 months: post V1: n = 17, post V2: n = 19; >3 months and <12 months: post V1: n = 19, post V2: n = 23; >12 months: post V1: n = 21, post V2: n = 34). The seroconversion rate after the second vaccination was significantly increased when the interval between the last anti-CD20 treatment and first vaccination was >12 months compared with an interval of 3 months to 12 months (68% vs 22%, Fisher’s exact test P = .001) or <3 months (68% vs 16%, Fisher’s exact test P < .001). (C) Multivariate logistic regression analysis for seroconversion after the second vaccination in anti-CD20-treated patients (complete case analysis, n = 50). Independent predictors for seroconversion were age (per 10 years, OR 0.5 [95% CI 0.2–0.8], P = .008), the interval between last anti-CD20 treatment and first vaccination (per year, OR 2.2 [95% CI 1.3–4.7], P = .02), and the CD4 T-cell count (per 100 cells/µL, OR 1.6 [95% CI 1.2–2.3], P = .005). (D) SARS-CoV-2 neutralizing capacity of anti-CD20-treated lymphoma patients according to the anti-S1-measured seroconversion. The neutralizing capacity of COVID-19 vaccine-induced antibodies was measured with a SARS-CoV-2 surrogate virus-neutralizing assay. Values were normalized to a negative control, and the inhibition capacity of the SARS-CoV-2 receptor binding domain: angiotensin-converting enzyme 2 interaction was expressed as a percentage. A cutoff of 30% inhibition was applied according to the manufacturer’s instructions and indicates the absence of a level of neutralizing antibodies below the limit of detection (represented by the dashed black line). The neutralizing antibody capacity was assessed in a subset of patients for whom additional samples were available (n = 38). Thirteen out of 15 patients (87%) with a positive anti-S1 antibody response had an inhibition exceeding the clinical cutoff for viral neutralization of 30%, whereas 22 out of 23 patients (96%) without seroconversion failed to achieve a successful neutralizing capacity. (E) SARS-CoV-2 neutralizing capacity of anti-CD20-treated lymphoma patients according to the interval between the last anti-CD20 treatment and first COVID-19 vaccination. The median neutralizing capacity after the second vaccination was significantly increased when the interval between the last anti-CD20 treatment and first vaccination was >12 months compared with an interval of 3 months to 12 months (12 months vs 3 months to 12 months: 86% [range 6% to 98%] vs 11% [range 4% to 23%], P = .002) or <3 months (12 months vs <3 months: 86% [range 6% to 98%] vs 21% [range 11% to 37%], P = .009). V1, vaccination 1; V2, vaccination 2; ns, not significant.