Previous studies have demonstrated low rates of seroconversion to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) messenger RNA (mRNA) vaccines in patients with chronic lymphocytic leukemia (CLL). In this national collaboration of 11 cancer centers in the United States, we aimed to further characterize and understand vaccine-induced immune responses, including T-cell responses, and the impact of CLL therapeutics (#NCT04852822). Eligible patients were enrolled in 2 cohorts (1) at the time of initial vaccination and (2) at the time of booster vaccination. The serologic response rates (anti-S) from 210 patients in the initial vaccination cohort and 117 in the booster vaccination cohort were 56% (95% confidence interval [CI], 50-63) and 68% (95% CI, 60-77), respectively. Compared with patients not on therapy, those receiving B-cell-directed therapy were less likely to seroconvert (odds ratio [OR], 0.27; 95% CI, 0.15-0.49). Persistence of response was observed at 6 months; anti-S
