HLA-DRB1 and COVID-19: The research on the influence of HLA genotype on COVID-19 severity revealed a significant difference in the allele frequency of HLA-DRB1*04:01 in severe patients as compared to the asymptomatic staff group in the European population (5.1% vs. 16.7%, p-value = 0.003 after adjustment for age and sex) [18].