Sandwich ELISA detection of recombinant Spike ECD protein(s) derived from different strains of SARS-CoV-2 virus (i.e.., Wild type; B1.617.2 delta variant; B.1.1.7 alpha variant; B.1.351 beta variant; P.1 gamma variant). SARS-CoV-2 (COVID-19) Spike RBD antibody [HL1014] used as capture antibody at concentration of 5 µg/mL and HRP-conjugated SARS-CoV-2 Spike Protein RBD monoclonal antibody (Product # MA5-46916) as detection antibody at concentration of 1 µg/mL. Please notice that MA5-46916 needs to be conjugated to HRP to function as the detection antibody when paired with SARS-CoV-2 (COVID-19) Spike RBD antibody [HL1014].