The SARS-CoV-2 (Omicron B.1.1.529) Spike Receptor Binding Domain (RBD) with Flag-His Tag is used in vaccine development and diagnostic assays to detect neutralizing antibodies against the Omicron variant of SARS-CoV-2. It serves as a key antigen in serological testing to evaluate immune response in infected or vaccinated individuals. The RBD is the portion of the spike protein that binds to the ACE2 receptor on human cells, playing a crucial role in viral entry mechanisms. The Flag and His tags enable easy detection and purification in experimental systems, such as ELISA for antibody detection or immunoprecipitation for studying protein interactions. It is employed in research focusing on antibody binding affinity and supports the development and validation of monoclonal antibodies for therapeutic use. Additionally, it enables structural analysis of spike protein interactions with host cell receptors.