RESUMO
The virus neutralization test (VNT) is the reference for the assessment of the functional ability of neutralizing antibodies (NAb) to block SARS-CoV-2 entry into cells. New competitive immunoassays measuring antibodies preventing interaction between the spike protein and its cellular receptor are proposed as surrogate VNT (sVNT). We tested three commercial sVNT (a qualitative immunochromatographic test and two quantitative immunoassays named YHLO and TECO) together with a conventional anti-spike IgG assay (bioMerieux) in comparison with an in-house plaque reduction neutralization test (PRNT50) using the original 19A strain and different variants of concern (VOC), on a panel of 306 sera from naturally-infected or vaccinated patients. The qualitative test was rapidly discarded because of poor sensitivity and specificity. Areas under the curve of YHLO and TECO assays were, respectively, 85.83 and 84.07 (p-value >0.05) using a positivity threshold of 20 for PRNT50, and 95.63 and 90.35 (p-value =0.02) using a threshold of 80. However, the performances of YHLO and bioMerieux were very close for both thresholds, demonstrating the absence of added value of sVNT compared to a conventional assay for the evaluation of the presence of NAb in seropositive subjects. In addition, the PRNT50 assay showed a reduction of NAb titers towards different VOC in comparison to the 19A strain that could not be appreciated by the commercial tests. Despite the good correlation between the anti-spike antibody titer and the titer of NAb by PRNT50, our results highlight the difficulty to distinguish true NAb among the anti-RBD antibodies with commercial user-friendly immunoassays.
RESUMO
With the availability of vaccines, commercial assays detecting anti-SARS-CoV-2 antibodies (Ab) evolved towards quantitative assays directed to the spike glycoprotein or its receptor binding domain (RBD). The main objective of the present study was to compare the Ab titers obtained with quantitative commercial binding Ab assays, after 1 dose (convalescent individuals) or 2 doses (naive individuals) of vaccine, in healthcare workers (HCW). Antibody titers were measured in 255 sera (from 150 HCW) with 5 quantitative immunoassays (Abbott RBD IgG II quant, bioMerieux RBD IgG, DiaSorin Trimeric spike IgG, Siemens Healthineers RBD IgG, Wantai RBD IgG). One qualitative total antibody anti RBD detection assay (Wantai) was used to detect previous infection before vaccination. The results are presented in binding Ab units (BAU)/mL after application, when possible, of a conversion factor provided by the manufacturers and established from a World Health Organization (WHO) internal standard. There was a 100% seroconversion with all assays evaluated after two doses of vaccine. With assays allowing BAU/ml correction, Ab titers were correlated (Pearson correlation coefficient, {rho}, range: 0.85-0.94). The titer differences varied by a mean of 10.6% between Siemens and bioMerieux assays to 60.9% between Abbott and DiaSorin assays. These results underline the importance of BAU conversion for the comparison of Ab titer obtained with the different quantitative assays. However, significant differences persist, notably, between kits detecting Ab against the different antigens. A true standardization of the assays would be to include the International Standard in the calibration of each assays to express the results in IU/mL.
RESUMO
BackgroundA comprehensive assessment of COVID-19 in healthcare workers (HCWs) including the investigation of viral shedding duration is critical. MethodsA longitudinal study including 319 HCWs was conducted. After SARS-CoV-2 screening with RT-PCR assay, other respiratory pathogens were tested with a multiplex molecular panel. For SARS-CoV-2 positive HCWs, the normalized viral load was determined weekly; viral culture and virus neutralization assays were also performed. For 190 HCWs tested negative, SARS-CoV-2 serological testing was performed one month after the inclusion. FindingsOf the 319 HCWs included, 67 (21.0%) were tested positive for SARS-CoV-2; two of them developed severe COVID-19. The proportion of smell and taste dysfunction was significantly higher in SARS-CoV-2 positive HCWs than in negative ones (38.8% vs 9.5% and 37.3% vs 10.7%, respectively, p<0.001). Of the 67 positive patients, 9.1% were tested positive for at least another respiratory pathogen (vs 19.5%, p=0.07). The proportion of HCWs with a viral load > 5.0 log10 cp/ml (Ct value <25) was less than 15% at 8 days after symptom onset; 12% of them were still positive after 40 days (Ct >37). More than 90% of culturable virus had a viral load > 4.5 log10 cp/ml (Ct < 26) and were collected within 10 days after symptom onset. From HCWs tested negative, 6/190 (3.2%) exhibited seroconversion for IgG antibodies. InterpretationOur data suggest that the determination of normalized viral load (or its estimation through Ct values) can be useful for discontinuing isolation of HCWs and facilitating their safe return to work. HCWs presenting mild COVID-19 are unlikely infectious 10 days after symptom onset. FundingFondation des Hospices Civils de Lyon. bioMerieux provided diagnostic kits.
