Because of the very rare occurrence of the 4c allele, and as the frequency of genotypes and alleles containing the c allele in the study groups was insufficient to warrant a statistical evaluation, we analyzed the association between NOS3 27-bp VNTR 4b/a genetic polymorphism and the progression of COVID-19 by excluding these two subjects with the 4c allele. Here, NOS3 is linked to COVID-19.