DPP9 and COVID-19: Haplotype frequency analysis revealed that the coexistence of CCL2 rs1024611-G, OAS1 rs10774671-A, and DPP9 rs10406145-G alleles in the same individual increased the presence of the severe COVID-19 phenotype (OR=2.273, 95% CI: 1.271-4.068, P=0.005305).