CD4 and HIV infectious disease: We studied the safety and immunogenicity of vaccination in participants with HIV on ART with CD4 counts of more than 350 cells per μL receiving two doses, 4–6 weeks apart, of a non-replicating chimpanzee adenovirus-vectored vaccine expressing the SARS-CoV-2 spike protein (ChAdOx1 nCoV-19), which has proven efficacy in people without HIV infection.1