Unvaccinated HLA-DRB1*01:01+ and HLA-A*0201 COVID-19 patients (n = 71) enrolled between January 2020 and December 2023, irrespective of the variant of concern with which they were infected, were divided into six groups based on the level of severity of their COVID-19 symptoms (increasing severity from 0 to 5), assessed at discharge (Fig. 2A). Here, HLA-A is linked to COVID-19.