An original multiplex method to assess five different SARS-CoV-2 antibodies.

Accurate SARS-CoV-2 serological assays are urgently needed to help diagnose infection, determine past exposure of populations and assess the response to future vaccines. The study aims at assessing the performance of the multiplex D-tek COVIDOT 5 IgG assay for the detection of SARS-CoV-2 IgG antibodies (N, S1+S2, S1, S2 and RBD). Sensitivity and dynamic trend to seropositivity were evaluated in 218 samples obtained from 46 rRT-PCR confirmed COVID-19 patients. Non-SARS-CoV-2 sera (n=118) collected before the COVID-19 pandemic with a potential cross-reaction to the SARS-CoV-2 immunoassay were included in the specificity analysis. A gradual dynamic trend since symptom onset was observed for all IgG antibodies. Sensitivities before day 14 were suboptimal. At ≥21 days, sensitivities reached 100% (93.4-100%) for N, S1+S2, S2 and RBD-directed IgG and 96.3% (87.3-99.6%) for S1-directed IgG. In 42 out of 46 patients (91.3%), all five antibodies were detected at ≥14 days. The four remaining patients had between 2 and 4 positive antibodies at their respective maximal follow-up period. The specificity was 100 % for S1+S2, S2 and RBD, 98.3% for N and 92.4% (86.0-96.5%) for S1-directed IgG. The combined use of antigens increases the early sensitivity whilst enforcing high specificity. Sensitivities at ≥21 days and specificities were excellent, especially for N, S1+S2, S2 and RBD-directed IgG. Caution is however required when interpreting single S1-directed reactivities. Using a multiplex assay complies with the orthogonal testing algorithm of the CDC and allows a better and critical interpretation of the serological status of a patient.

Favresse J ，Brauner J ，Bodart N ，Vigneron A ，Roisin S ，Melchionda S ，Douxfils J ，Ocmant A ... -  《-》

Multiplex assessment of SARS-CoV-2 antibodies improves assay sensitivity and correlation with neutralizing antibodies.

Detection of antibodies to multiple SARS-CoV-2 antigens in a single assay could increase diagnostic accuracy, differentiate vaccination from natural disease, and aid in retrospective exposure determination. Correlation of binding antibody assessment in clinical assays with neutralizing antibodies is needed to better understand the humoral response to SARS-CoV-2 infection and establish of correlates of protection. A cohort of 752 samples was used to assess specificity, sensitivity, and comparison to 6 other Conformitè Europëenne serologic assays for the BioRad SARS-CoV-2 IgG multiplex assay which measures receptor binding domain IgG (RBD), spike-S1 IgG (S1), spike-S2 IgG (S2), and nucleocapsid IgG (N). A subset of serial specimens from 14 patients was also tested for neutralizing antibodies (n = 61). Specificity for RBD and S1 IgG was 99.4% (n = 170) and 100% for S2 and N IgG (n = 170) in a cohort selected for probable interference. Overall assay concordance with other assays was >93% for IgG and total antibody assays and reached 100% sensitivity for clinical concordance at >14 days as a multiplex assay. RBD and S1 binding antibody positivity demonstrated 79-95% agreement with the presence of neutralizing antibodies. The BioRad SARS-CoV-2 IgG assay is comparable to existing assays, and achieved 100% sensitivity when all markers were included. The ability to measure antibodies against spike and nucleocapsid proteins simultaneously may be advantageous for complex clinical presentations, epidemiologic research, and in decisions regarding infection prevention strategies. Additional independent validations are needed to further determine binding antibody and neutralizing antibody correlations.

Cook N ，Xu L ，Hegazy S ，Wheeler BJ ，Anderson AR ，Critelli N ，Yost M ，McElroy AK ，Shurin MR ，Wheeler SE ... -  《-》

Determination of SARS-CoV-2 antibodies with assays from Diasorin, Roche and IDvet.

There is an ongoing need for highly reliable serological assays to detect individuals with past SARS-CoV-2 infection. Using 75 sera from patients tested positive or negative by SARS-CoV-2 PCR, we investigated the sensitivity and specificity of the Liaison SARS-CoV-2 S1/S2 IgG assay (DiaSorin), the Elecsys Anti-SARS-CoV-2 assay (Roche), and the ID Screen SARS-CoV-2-N IgG indirect kit (IDVet). We determined a sensitivity of 95.5 %, 95.5 %, and 100 % and a specificity of 90.5 %, 96.2 %, and 92.5 % for the DiaSorin assay, the Roche assay, and the IDVet assay, respectively. We conclude that serologic assays combining very high sensitivity and specificity are still not commercially available for SARS-CoV-2. For maximizing sensitivity and specificity of SARS-CoV-2 serological diagnostics, the combination of two assays may be helpful.

Krüttgen A ，Cornelissen CG ，Dreher M ，Hornef MW ，Imöhl M ，Kleines M ... -  《-》

Analytical characterization of the SARS-CoV-2 EURM-017 reference material.

Current serological methods for SARS-CoV-2 lack adequate standardization to a universal standard reference material. Standardization will allow comparison of results across various lab-developed and commercial assays and publications. SARS-CoV-2 EURM-017 is human sera reference material containing antibodies directed against SARS-CoV-2 proteins, S1/S2 (full-length spike [S]), S1 receptor-binding domain (S1 RBD), S1, S2, and nucleocapsid (N) protein. The goal of this study was to characterize five antigen-specific serum fractions in EURM-017 for standardization of serology assays. Five antigen-specific serum fractions were affinity purified, quantified, and PRNT50 titers compared. Standardization methods were established for two anti-S1 RBD (IgG and Total Ig) and one N protein assay. For the anti-S1 RBD assays, standardization involved determining assay index values for serial dilutions of S1-RBD anti-sera. Index values for the anti-S1 RBD IgG assay and PRNT50 titers were determined for 44 symptomatic COVID-19 patient sera. The index values were converted to EURM-017 ug/mL. Anti-sera protein content was as follows: S1 (17.7 µg/mL), S1 RBD (17.4 µg/mL), S1/S2 (full-length S) (34.1 µg/mL), S2 (29.7 µg/mL), and N protein (72.5 µg/mL). S1 anti-serum had the highest neutralization activity. A standardization method for S1 RBD anti-serum and an anti-S1 RBD IgG assay yielded the linear equation (y = 0.75x-0.10; y = index, x=µg/mL anti-serum). Patient sample index values for the S1-RBD IgG assay correlated well with PRNT50 titers (Pearson r = 0.84). Using the equation above, patient index values were converted to standardized µg/mL. Standardization of different lab-developed and commercial assays to EURM-017 antigen-specific anti-sera will allow comparison of results across studies globally due to traceability to a single standard reference material.

Freeman J ，Olson K ，Conklin J ，Shalhoub V ，Johnson BA ，Bopp NE ，Fernandez D ，Menachery VD ，Aguilar PV ... -  《-》

A Serological Snapshot of COVID-19 Initial Stages in Israel by a 6-Plex Antigen Array.

Fisher M ，Levy H ，Fatelevich E ，Afrimov Y ，Ben-Shmuel A ，Rosenfeld R ，Noy-Porat T ，Glinert I ，Sittner A ，Biber A ，Belkin A ，Bar-David E ，Puni R ，Levy I ，Mazor O ，Weiss S ，Mechaly A ... -  《Microbiology Spectrum》