Moreover, the immune sera from mice immunized with CCD-adjuvanted RBD-HR broadly protected against infection with both the wild-type (WT) and common mutant strains of SARS-CoV-2, including Alpha, Beta, Delta, and Omicron variants (BA.1, BA.2, BA.2.12.1, BA.3, and BA.4/5) (Fig. 2e)21. This evidence concerns the gene HR and infection.