The SARS-CoV-2 (Omicron BA.2) Spike RBD protein with His Tag is used in vaccine development and antibody testing due to its critical role in viral entry. The His Tag enables easy purification and detection. It facilitates the study of immune responses against the Omicron variant, supports diagnostic assay design, therapeutic antibody screening, and serves as a key target for evaluating neutralizing antibodies and vaccine efficacy.