Protein-based RBD-C-tag COVID-19 Vaccination Candidate Elicits Protection Activity against SARS-COV-2 Variant Infection

The identification of a vaccination candidate against COVID-19 providing protecting activity against emerging SARS-COV-2 variants remains challenging. Here, we report protection activity against a spectrum of SARS-COV-2 and variants by immunization with protein-based recombinant RBD-C-tag administered with aluminum-phosphate adjuvant intramuscularly. Immunization of C57BL/6 mice with RBD-C-tag resulted in the in vivo production of IgG antibodies recognizing the immune-critical spike protein of the SARS-COV-2 virus as well as the SARS-COV-2 variants alpha ("United Kingdom"), beta ("South Africa"), gamma ("Brazil/Japan"), and delta ("India") as well as wt-spike protein. RBD-C-tag immunization led to a desired Th1 polarization of CD4 T cells producing IFN{gamma}. Importantly, RBD-C-tag immunization educated IgG production delivers antibodies that exert neutralizing activity against the highly transmissible SARS-COV-2 virus strains "Washington", "South Africa" (beta), and "India" (delta) as determined by conservative infection protection experiments in vitro. Hence, the protein-based recombinant RBD-C-tag is considered a promising vaccination candidate against COVID-19 and a broad range of emerging SARS-COV-2 virus variants.