Clinical Research Directory

Inclusion Criteria: * NAIVE COHORT: Subjects must have a confirmed diagnosis of chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL) (collectively referred to as CLL throughout) according to the 2018 International Workshop on CLL. * NAIVE COHORT: Male or female subject aged \>= 18 years. * NAIVE COHORT: Subjects must not have received prior therapy for CLL. * VENETOCLAX-TREATMENT COHORT: Subjects must have a confirmed diagnosis of chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL) (collectively referred to as CLL throughout) according to the 2018 International Workshop on CLL. * VENETOCLAX-TREATMENT COHORT: Subjects must have received venetoclax (any dose) for at least 12 months with the last dose =\< 12 months prior to registration. Exclusion Criteria: * Subjects who have experienced a severe allergic reaction to prior pneumococcal vaccination. * Subjects who have received a PCV13 or PCV20 pneumococcal vaccination in the last five years. * If they have received PPSV23 in ≥ 1 year and no other pneumococcal vaccine they may be included. * Active infection requiring systemic antibiotic therapy. * Current or prior use of immunosuppressive medication within 14 days of cycle one day one, EXCEPT for the following permitted steroids: * Intranasal, inhaled, topical steroids, eye drops or local steroid injection (e.g., intra-articular injection); * Systemic corticosteroids at physiologic doses =\< 10 mg/day of prednisone or equivalent; * Steroids as premedication for hypersensitivity reactions (e.g., computed tomography \[CT\] scan premedication). * Concurrent illness or condition, which, in the opinion of the treating investigator, would negatively impact the subject's study participation.