Sandwich ELISA detection of recombinant Spike ECD protein(s) derived from different strains of SARS-CoV-2 virus (ie., Wild type; B.1.1.7 alpha variant; B.1.351 beta variant; P.1 gamma variant; B1.617.2 delta variant) using antibodies as below. Capture: SARS-CoV / SARS-CoV-2 (COVID-19) spike antibody [1A9] (GTX632604) (5 μg/mL) Detection: SARS-CoV-2 (COVID-19) Spike RBD antibody [HL1003] (GTX635792) (1 μg/mL)