On the contrary, blood samples from healthy donors (Naïve group) who were never affected by COVID-19 and were not vaccinated, were mainly characterized by the presence of Mature NK cells, which are the cell subset in the final stages of development, with the acquisition of functional competence in cytotoxicity and production of interferon (IFN)-γ [14, 28, 29]. Here, IFNG is linked to COVID-19.