RESUMO
We conducted a prospective study in healthcare workers (n=296) of the University Hospital of Lyon, France. Serum samples (n=296) collected six months after disease onset were tested using three commercial assays: the Wantai Ab assay detecting total antibodies against the receptor binding domain (RBD) of the S protein, the bioMerieux Vidas assay detecting IgG to the RBD and the Abbott Architect assay detecting IgG to the N protein. The neutralising antibody (NAb) titre was also determined for all samples with a virus neutralisation assay (VNA) using live virus. The positivity rate was 100% with the Wantai assay, 84.8% with the bioMerieux assay and 55.4% with the Abbott assay. Only 51% of HCWs were positive for the presence of NAb. Less than 10 % of HCWs had a NAb titre greater than 80. At a neutralising titre of 80, the area under the curves [IC 95%] was 0.71 [0.62-0.81], 0.75 [0.65-0.85] and 0.95 [0.92-0.97] for Wantai, Abbott and Vidas respectively. The data presented herein suggest that commercial assays detecting antibodies against the N protein must not be used in long-term seroprevalence surveys while the Wantai assay could be useful for this purpose. VNA should remain the gold standard to assess the protective antibody response, but some commercial assays could be used as first-line screening of long-term presence of NAb.
RESUMO
ObjectivesWe evaluated widely-used SARS-CoV-2 serological tests and their potential association with virus neutralization test (VNT) in a cohort of mild COVID-19 patients. MethodsA total of 439 specimens were longitudinally collected from 76 healthcare workers with RT-PCR-confirmed mild COVID-19. Nine serological assays developed by leading global companies (Abbott, DiaSorin, Siemens, Bio-Rad, Wantai, bioMerieux, Euroimmun) were assessed. For each test the sensitivity to detect SARS-CoV-2 antibodies was determined weekly after symptom onset. Correlation and concordance were assessed using the Spearman and Cohens Kappa coefficients, respectively. Positive percent agreement and negative percent agreement (NPA) with the VNT were also determined. ResultsThe Wantai Total Ab assay targeting the receptor binding domain (RBD) within the S protein presented the best sensitivity at different times during the course of disease. The best correlation between antibody level and neutralizing antibody titer was found with the Euroimmun S1-based IgA assay (Spearman coefficient [95%CI]: 0.71 [0.61-0.79]). A moderate concordance (Kappa [95%CI]: 0.43[0.23-0.63]) as well as the lowest NPA (33%) was found between the Wantai Total Ab assay and the VNT. Compared to the Wantai Total Ab assay, other total Ab or IgG assays targeting the S or the RBD (bioMerieux, DiaSorin, Siemens,) were more concordant with the VNT (Kappa>0.7 for the three tests) and had a higher NPA (range: 90% to 97%). ConclusionsAlthough some assays presented a better concordance with VNT than others, the present findings emphasize that commercialized serological tests including those targeting the RBD cannot substitute VNT for the assessment of functional antibody response.
