marginally significantP =0.05
Moreover, no correlation was found between either the RBD or NAb titer at T2 with T- and B-lymphocyte subpopulations, except for a marginally significant positive correlation of NAb titers with the CD4 + CD28 – CD57 + percentage (BC=0.359, R 2 =0.129, P =0.05) at T2.