CDCA7L and COVID-19: In human COVID-19 convalescent and vaccinated populations, rare nAbs targeting HR1 and HR2 domains in the S2 subunit were isolated.33,57 Here, we detected moderate levels of anti-HR1, -HR2, and -HR12 antibodies in the sera of these individuals (Fig. 2h), which is consistent with the results of a previous report.58 However, none of their sera could inhibit the binding between HR2 and HR121 in the competitive ELISA (Fig. 2i; Supplementary information, Fig. S3g, h), implying that few nAbs targeting membrane fusion could be generated from these populations.