MICB and COVID-19: The present work aimed to assess the effect of genetic variability in genes coding for NKG2 receptors (NKG2A, NKG2C, and NKG2D), as well as their ligands (HLA-E, MICA, MICB), and the serum concentrations of these ligands on the incidence of SARS-CoV-2 infection and severity of COVID-19 in representatives of the Polish population.