The magnitude of the SARS-CoV-2-specific IFN-γ-positive T cell response was significantly lower in those reporting a positive COVID-19 diagnostic test than uninfected donors (P < 0.0001; Fig. 2a), predominantly due to sub-optimal induction of T cell responses by vaccination amongst certain participants (P = 0.050; Supplementary Fig. 1). This evidence concerns the gene IFNG and COVID-19.