CD4 and COVID-19: Percentages of CD4+, Th17, Treg cells and the Th17/Treg ratio were not significantly different between vaccine timing groups (0-3 months, 3-6 months, 6-9 months, 9-12 months, > 12 months between COVID-19 vaccination and sampling) and a reference group of never vaccinated participants (Supplementary Figure 4B; Supplementary Table 4B).