Additionally, some important hub-high traffic genes involved in the cytotoxic activity of natural killer cells during COVID-19 were NCAM1 (252, 282), GZMA, NKG7 (283, 284), KLRD1 (285, 286), GZMB (150, 287, 288), and PRF1 (289–291). This evidence concerns the gene KLRD1 and COVID-19.