The SARS-CoV-2 (Omicron B.1.1.529) Spike RBD protein features mutations F375S and A484E, which enhance immune evasion capabilities. Fused with an Fc tag for facile detection and purification, it is used in vaccine development, diagnostic assays, and studies of immune responses against the Omicron variant. Suitable for binding assays (e.g., with ACE2 receptor), neutralization studies, evaluation of monoclonal antibodies and therapeutics, assessment of vaccine/serum efficacy, and screening of potential inhibitors.