SARS-CoV-2 specific antibody responses in COVID-19 patients

NISREEN M.A. OKBA; Marcel A Muller; Wentao Li; Chunyan Wang; Corine H. GeurtsvanKessel; Victor M. Corman; Mart M. Lamers; Reina S. Sikkema; Erwin de Bruin; Felicity D. Chandler; Yazdan Yazdanpanah; Quentin Le Hingrat; Diane Descamps; Nadhira Houhou-Fidouh; Chantal B. E. M. Reusken; Berend-Jan Bosch; Christian Drosten; Marion P.G. Koopmans; Bart L. Haagmans

We performed Anti-SARS-CoV-2 IgG and IgA ELISA using beta-versions of two commercial kits (EUROIMMUN Medizinische Labordiagnostika AG, https://www.euroimmun.com) and performed the assay according to manufacturer's protocol. Reagent wells of both assays are coated with recombinant structural protein (S1 domain) of SARS-CoV-2. The optical density (OD) was detected at 450 nm, and a ratio of the reading of each sample to the reading of the calibrator, included in the kit, was calculated for each sample (OD ratio). As the beta-version of the kit awaits CE validation, we determined an in-house cut-off value based on the mean background reactivity of all SARS-CoV-2-negative sera in the study multiplied by 3. In case of IgA this was OD ratio = 0.9 and for IgG OD ratio = 0.3.