Enhanced CD4+ T-cell frequencies after 3 vaccine doses were also associated with male sex, having received mRNA-1273 as a third vaccine dose, and−somewhat surprisingly–the presence of chronic health conditions (omitting cancer or blood disorders), although these correlates were all weaker than the post-second-dose T-cell responses (estimates 0.23–0.29; P=0.007 to 0.03; Supplementary Table 2). Here, CD4 is linked to cancer.