PWH with a breakthrough COVID-19 illness who had a CD4 cell count of less than 200 cells/μL (9 of 54 patients [16.7%]) and 200 to 349 cells/μL(17 of 109 patients [15.6%]) were less likely to receive an additional vaccine dose, compared with PWH with CD4 cell counts greater than or equal to 350 cells/μL(182 of 899 patients [20.5%]) (eTable 3 in the Supplement). Here, CD4 is linked to COVID-19.