• Victoria Indenbaum, Ravit Koren, Shiri Katz-Likvornik, Mayan Yitzchaki, Osnat Halpern, Gili Regev-Yochay, Carmit Cohen, Asaf Biber, Tali Feferman, Noy Cohen Saban, Roni Dhan, Tal Levin, Yael Gozlan, Merav Weil, Orna Mor, Michal Mandelboim, Danit Sofer, Ella Mendelson, and Yaniv Lustig.
• Central Virology Laboratory and Sheba Medical Center, Ministry of Health, Tel-Hashomer, Israel.
• Plos One. 2020 Jan 1; 15 (11): e0241164.

AbstractThe COVID-19 pandemic and the fast global spread of the disease resulted in unprecedented decline in world trade and travel. A critical priority is, therefore, to quickly develop serological diagnostic capacity and identify individuals with past exposure to SARS-CoV-2. In this study serum samples obtained from 309 persons infected by SARS-CoV-2 and 324 of healthy, uninfected individuals as well as serum from 7 COVID-19 patients with 4-7 samples each ranging between 1-92 days post first positive PCR were tested by an "in house" ELISA which detects IgM, IgA and IgG antibodies against the receptor binding domain (RBD) of SARS-CoV-2. Sensitivity of 47%, 80% and 88% and specificity of 100%, 98% and 98% in detection of IgM, IgA and IgG antibodies, respectively, were observed. IgG antibody levels against the RBD were demonstrated to be up regulated between 1-7 days after COVID-19 detection, earlier than both IgM and IgA antibodies. Study of the antibody kinetics of seven COVID 19 patients revealed that while IgG levels are high and maintained for at least 3 months, IgM and IgA levels decline after a 35-50 days following infection. Altogether, these results highlight the usefulness of the RBD based ELISA, which is both easy and cheap to prepare, to identify COVID-19 patients even at the acute phase. Most importantly our results demonstrate that measuring IgG levels alone is both sufficient and necessary to diagnose past exposure to SARS-CoV-2.

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