Evaluation of nine commercial SARS-CoV-2 immunoassays

Ria Lassaunière; Anders Frische; Zitta B Harboe; Alex CY Nielsen; Anders Fomsgaard; Karen A Krogfelt; Charlotte S Jørgensen

The differences between the assays may, in part, be explained by the SARS-CoV-2 antigen targeted and the ELISA format used. Both kits detect antibodies to the S1 subunit of the SARS-CoV-2 spike protein; however, the Wantai Total Ab ELISA only targets the RBD within the S1. The RBD represents approximately 33% of the S1 subunit, thus epitopes that may be recognized by cross-reacting epitopes outside of this domain are absent. Furthermore, the RBD is highly diverse between SARS-CoV-2 and other beta-coronaviruses (hCoV-OC43 and hCoV-HKU1), which may further reduce the likelihood of cross-reaction with these circulating coronaviruses. Moreover, the Wantai Total Ab ELISA uses an antigen-antibody-antigen(peroxidase) format whereas the Euroimmun ELISAs employ an antigen-antibody-antibody(peroxidase) format. The specificity of the former is determined by a single antibody, whereas the latter has a second antibody that may introduce additional specificities. The antigen-antibody-antibody format is required to distinguish between specific antibody types, but may not necessarily have lead to decreased specificity as shown for in-house ELISAs [10].