Used in research and development of COVID-19 vaccines, particularly for the Omicron (B.1.1.529) variant, due to the Spike S1 protein's crucial role in binding to host cells. This makes it ideal for studying immune responses, developing specific antibodies, testing vaccine efficacy, and assessing antibody levels in blood samples. The Avi-His Tag enables easy binding to intermediates, facilitating efficient use in ELISA techniques, purification by chromatography, and various detection systems.