ACE2 and COVID-19: To further confirm whether these anti-ACE2 IgG antibodies encompassed CR Abs, sera from COVID-19 patients with OD values of anti-ACE2 IgG exceeding 0.39, as determined by the cutoff value (> 2.1 fold of OD values of anti-ACE2 IgG in unvaccinated individuals), were selected for BSA or RBD preadsorption ELISAs.