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Red cells can be labelled with peptides from the SARS-CoV-2 spike protein and used for serologic screening of SARS-CoV-2 antibodies. We evaluated 140 convalescent COVID-19 patients and 275 healthy controls using this C19-kodecyte assay. The analytical performance of the new assay was compared with a virus neutralizing assay and 2 commercial chemiluminescent antibody tests (Total assay and IgG assay, Ortho). The C19-kodecyte assay detected SARS-CoV-2 antibodies with a sensitivity of 92.8% and specificity of 96.3%, well within the minimum performance range required by FDA for EUA authorization of serologic tests. The Cohens kappa coefficient was 0.90 indicating an almost perfect agreement with the Total assay. The Pearson correlation coefficient was 0.20 with the neutralizing assay (0.49 with IgG, and 0.41 with Total assays). The limited correlation in assay reaction strengths suggested that the assays may detect different antibody specificities. Our easily scalable C19-kodecyte assay may vastly improve test capacity in blood typing laboratories using their routine setups for column agglutination technique.
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BackgroundCharacterizing the kinetics of the antibody response to SARS{square}CoV{square}2 is of critical importance to developing strategies that may mitigate the public health burden of COVID-19. We sought to determine how circulating antibody levels change over time following natural infection. Methods/MaterialsWe conducted a prospective, longitudinal analysis of COVID-19 convalescent plasma (CCP) donors at multiple time points over a 9-month period. At each study visit, subjects either donated plasma or only had study samples drawn. In all cases, anti-SARS-CoV-2 donor testing was performed using semi-quantitative chemiluminescent immunoassays (ChLIA) targeting subunit 1 (S1) of the SARS-CoV-2 spike (S) protein, and an in-house fluorescence reduction neutralization assay (FRNA). ResultsFrom April to November 2020 we enrolled 202 donors, mean age 47.3 {+/-}14.7 years, 55% female, 75% Caucasian. Most donors reported a mild clinical course (91%, n=171) without hospitalization. One hundred and five (105) (52%) donors presented for repeat visits with a median 42 (12-163) days between visits. The final visit occurred at a median 160 (53-273) days post-symptom resolution. Total anti-SARS-CoV-2 antibodies (Ab), SARS-CoV-2 specific IgG and neutralizing antibodies were detected in 97.5%, 91.1%, and 74% of donors respectively at initial presentation. Neutralizing Ab titers based on FRNA50 were positively associated with mean IgG levels (p = <0.0001). Mean IgG levels and neutralizing titers were positively associated with COVID-19 severity, increased donor age and BMI (p=0.0006 and p=0.0028, p=0.0083 and p=0.0363, (p=0.0008 and p=0.0018, respectively). Over the course of repeat visits, IgG decreased in 74.1% of donors; FRNA50 decreased in 44.4% and remained unchanged in 33.3% of repeat donors. A weak negative correlation was observed between total Ab levels and number of days post-symptom recovery (r = 0.09). ConclusionAnti-SARS-CoV-2 antibodies were identified in 97% of convalescent donors at initial presentation. In a cohort that largely did not require hospitalization. IgG and neutralizing antibodies were positively correlated with age, BMI and clinical severity, and persisted for up to 9 months post-recovery from natural infection. On repeat presentation, IgG anti-SARS-CoV-2 levels decreased in 56% of repeat donors. Overall, these data suggest that CP donors possess a wide range of IgG and neutralizing antibody levels that are proportionally distributed across demographics, with the exception of age, BMI and clinical severity.
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To date severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has infected over 100 million individuals resulting in over two million deaths. Many vaccines are being deployed to prevent coronavirus disease 2019 (COVID-19) including two novel mRNA-based vaccines1,2. These vaccines elicit neutralizing antibodies and appear to be safe and effective, but the precise nature of the elicited antibodies is not known3-6. Here we report on the antibody and memory B cell responses in a cohort of 20 volunteers who received either the Moderna (mRNA-1273) or Pfizer-BioNTech (BNT162b2) vaccines. Consistent with prior reports, 8 weeks after the second vaccine injection volunteers showed high levels of IgM, and IgG anti-SARS-CoV-2 spike protein (S) and receptor binding domain (RBD) binding titers3,5,6. Moreover, the plasma neutralizing activity, and the relative numbers of RBD-specific memory B cells were equivalent to individuals who recovered from natural infection7,8. However, activity against SARS-CoV-2 variants encoding E484K or N501Y or the K417N:E484K:N501Y combination was reduced by a small but significant margin. Consistent with these findings, vaccine-elicited monoclonal antibodies (mAbs) potently neutralize SARS-CoV-2, targeting a number of different RBD epitopes in common with mAbs isolated from infected donors. Structural analyses of mAbs complexed with S trimer suggest that vaccine- and virus-encoded S adopts similar conformations to induce equivalent anti-RBD antibodies. However, neutralization by 14 of the 17 most potent mAbs tested was reduced or abolished by either K417N, or E484K, or N501Y mutations. Notably, the same mutations were selected when recombinant vesicular stomatitis virus (rVSV)/SARS-CoV-2 S was cultured in the presence of the vaccine elicited mAbs. Taken together the results suggest that the monoclonal antibodies in clinical use should be tested against newly arising variants, and that mRNA vaccines may need to be updated periodically to avoid potential loss of clinical efficacy.