Notably, only a small portion of double-positive (IFN-γ+TNF+) CD8+ T cells were observed in S/M/N/E+CD8+ and RBD+CD8+ T cells among all four groups, indicating that the virus-specific CD8+ T cells induced by breakthrough infection and three-dose inactivated vaccine lacked multiple functions (Fig. 3f). The gene discussed is TNF; the disease is infection.