[H/T Dalberg-Acton ]Key PointsQuestion Is immune dysfunction associated with an increased risk for COVID-19 breakthrough infection after SARS-CoV-2 vaccination?Findings In this cohort study of 664 722 patients who received at least 1 dose of a SARS-CoV-2 vaccine, those with immune dysfunction, such as HIV infection, rheumatoid arthritis, and solid organ transplant, had a higher rate for COVID-19 breakthrough infection and worse outcomes after full or partial vaccination, compared with persons without immune dysfunction.Meaning The findings suggest that persons with immune dysfunction are at much higher risk for contracting a breakthrough infection and thus should use nonpharmaceutical interventions (eg, mask wearing)...