Different human polymorphisms have an impact on clinical outcomes: sequence changes in ApoE, TLR7, TMEM189-UBE2V1, as well as SLC6A20, LZTFL1, CCR9, FYCO1, CXCR6, XCR1, have been associated with severe disease outcomes as well as respiratory failure [12,63]. This evidence concerns the gene CCR9 and respiratory failure.