CD4 and COVID-19: Analysis of vaccine effectiveness in terms of prevented hospital admissions and protection against disease progression to moderate or severe forms of COVID-19 shows that in patients with CD4+ T-cell counts ≥ 350 cells/μl the vaccine averted hospitalization in 100% of the group during the first period and in 75·77% (95% CI 44·25–89·47%) during the second (with predominant occurrence of the delta variant).