The first GWAS analysis with 1980 patients with COVID-19 identified two loci associated with the most severe forms of COVID-19: one locus was 3p21.31, which includes the genes SLC6A20, LZTFL1, CCR9, FYCO1, CXCR6, and XCR1, while the other was 9q34.21, including the ABO blood group. Here, CCR9 is linked to COVID-19.