As the PBMCs were cultured at the same density and in the same media for both assays (TexMACS), the differences are likely due to the sensitivity of the assay formats used by proprietary FluoroSpot and ELISA kits, as well as the high IFN-γ background observed using FluoroSpot analysis in some people after COVID-19 [65]. This evidence concerns the gene IFNG and COVID-19.