ABSTRACT
ObjectivesVarious commercial anti-Spike SARS-CoV-2 antibody tests are used for studies and in clinical settings after vaccination. An international standard for SARS-CoV-2 antibodies has been established to achieve comparability of such tests, allowing conversions to BAU/ml. This study aimed to investigate the comparability of antibody tests regarding the timing of blood collection after vaccination. MethodsFor this prospective observational study, antibody levels of 50 participants with homologous AZD1222 vaccination were evaluated at 3 and 11 weeks after the first dose and 3 weeks after the second dose using two commercial anti-Spike binding antibody assays (Roche and Abbott) and a surrogate neutralization assay. ResultsThe correlation between Roche and Abbott changed significantly depending on the time point studied. Although 3 weeks after the first dose, Abbott provided values three times higher than Roche, 11 weeks after the first dose, the values for Roche were twice as high as for Abbott, and 3 weeks after the second dose even 5-6 times higher. ConclusionsThe comparability of quantitative anti-Spike SARS-CoV-2 antibody tests is highly dependent on the timing of blood collection after vaccination. Therefore, standardization of the timing of blood collection might be necessary for the comparability of different quantitative SARS-COV-2 antibody assays. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=175 SRC="FIGDIR/small/21262426v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@1e789daorg.highwire.dtl.DTLVardef@b83aforg.highwire.dtl.DTLVardef@1f270daorg.highwire.dtl.DTLVardef@1cf296c_HPS_FORMAT_FIGEXP M_FIG C_FIG
ABSTRACT
ObjectivesOur objective was to determine whether SARS-CoV-2 antibody levels after the first dose can predict the final antibody response and whether this is dependent on the vaccine type. Methods69 BNT162b2 (Pfizer/BioNTech) and 55 AZD1222 (AstraZeneca) vaccinees without previous infection or immunosuppressive medication were included. Anti-body levels were quantified 3 weeks after dose 1, in case of AZD1222 directly before boostering (11 weeks after dose 1) and 3 weeks after dose 2, with the Roche SARS-CoV-2 S total antibody assay. ResultsPre-booster (BNT162b2: 80.6 [25.5-167.0] BAU/mL, AZD1222: 56.4 [36.4-104.8] BAU/mL, not significant) and post-booster levels (BNT162b2: 2,092.0 [1,216.3-4,431.8] BAU/mL, AZD1222: 957.0 [684.5-1,684.8] BAU/mL, p<0.0001) correlated well in BNT162b2 ({rho}=0.53) but not in AZD1222 recipients. Moreover, antibody levels after the first dose of BNT162b2 correlated inversely with age ({rho}=-0.33, P=0.013), whereas a positive correlation with age was observed after the second dose in AZD1222 recipients ({rho}=0.26, P=0.030). ConclusionsIn conclusion, our data suggest that antibody levels quantified by the Roche Elecsys SARS-CoV-2 S assay before the booster shot could infer post-booster responses to BNT162b2, but not to AZ1222. In addition, we found a vaccine-dependent effect on antibody responses, suggesting a possible link between vaccine response and vector immunity.
ABSTRACT
ObjectivesSARS-CoV-2 infection induces the formation of different antibodies. However, not all of which might prevent the virus from entering the cell, although their concentrations correlate with the titers of viral neutralization tests (NTs). Antibodies against the viral nucleocapsid (NC), e.g., can be classified as such. We aimed to prove the hypothesis that the apparent correlation between NC-antibody levels and NT-titers is mediated by simultaneously occurring antibodies against viral spike-protein components. MethodsWe included 64 individuals with previous SARS-CoV-2 infection (>14d after symptom onset). SARS-CoV-2 antibodies against the NC (Roche total antibody ECLIA, Abbott IgG CMIA) and spike-protein (Technozym RBD ELISA, DiaSorin S1/S2 CLIA) were measured, and neutralization tests were performed. The effect of spike-protein antibodies on the correlation between NC-antibodies and NT-titers was evaluated by partial correlation and mediation analyses. ResultsBoth tested assays assessing antibodies against the NC correlated significantly with NT titers: Abbott {rho}=0.742, P<0.0001; Roche {rho}=0.365, P<0.01. However, when controlling the rank correlations for the presence of RBD or S1/S2 antibodies, correlation coefficients dropped to {rho}=0.318/{rho}=0.329 (P<0.05/P<0.01), respectively for Abbott and vanished for Roche. As a result, only a maximum of 11% of NT titer variability could be explained by NC-antibody levels. ConclusionsOur data suggest that the apparent correlation between NC antibodies and NT titers is strongly mediated by co-occurring RBD antibody concentrations. To avoid falsely implied causal relationships, all correlation analyses of non-spike-associated antibody assays and neutralization assays should include a partial correlation analysis to exclude a possible mediator effect of spike-associated antibodies.
ABSTRACT
BackgroundReliable quantification of the antibody response to SARS-CoV-2 vaccination is highly relevant for identifying possible vaccine failure and estimating the time of protection. Therefore, we aimed to evaluate the performance of five different Anti-SARS-CoV-2 antibody assays regarding the quantification of anti-spike (S) antibodies induced after a single dose of BNT162b2. MethodsSera of n=69 SARS-CoV-2 naive individuals 21{+/-}1 days after vaccination with BNT162b2 (Pfizer/BioNTech) were tested using the following quantitative SARS-CoV-2 antibody assays: Roche S total antibody, DiaSorin trimeric spike IgG, DiaSorin S1/S2 IgG, Abbott II IgG, and Serion/Virion IgG. Test agreement was assessed by Passing-Bablok regression. Results were further compared to the percent inhibition calculated from a surrogate virus neutralization test (sVNT) by correlation and ROC (receiver-operating-characteristics) analysis. ResultsIndividual values were distributed over several orders of magnitude for all assays evaluated. Although the assays were in good overall agreement ({rho}=0.80-0.94), Passing-Bablok regression revealed systematic and proportional differences, which could not be eliminated by converting the results to BAU/mL as suggested by the manufacturers. 7 (10%) individuals had a negative sVNT results (i.e. <30% inhibition). These samples were reliably identified by most assays and yielded low binding antibody levels (ROC-AUCs 0.84-0.93). ConclusionsAlthough all assays evaluated showed good correlation, readings from different assays were not interchangeable, even when converted to BAU/mL using the WHO international standard for SARS-CoV-2 immunoglobulin. This highlights the need for further standardization of SARS-CoV-2 serology.
ABSTRACT
BackgroundSerological tests are widely used in various medical disciplines for diagnostic and monitoring purposes. Unfortunately, the sensitivity and specificity of test systems is often poor, leaving room for false positive and false negative results. However, conventional methods used to increase specificity decrease sensitivity and vice versa. Using SARS-CoV-2 serology as an example, we propose here a novel testing strategy: the "Sensitivity Improved Two-Test" or " SIT2" algorithm. MethodsSIT2 involves confirmatory re-testing of samples with results falling in a predefined retesting-zone of an initial screening test, with adjusted cut-offs to increase sensitivity. We verified and compared the performance of SIT2 to single tests and orthogonal testing (OTA) in an Austrian cohort (1,117 negative, 64 post-COVID positive samples) and validated the algorithm in an independent British cohort (976 negatives, 536 positives). ResultsThe specificity of SIT2 was superior to single tests and non-inferior to OTA. The sensitivity was maintained or even improved using SIT2 when compared to single tests or OTA. SIT2 allowed correct identification of infected individuals even when a live virus neutralization assay could not detect antibodies. Compared to single testing or OTA, SIT2 significantly reduced total test errors to 0.46% (0.24-0.65) or 1.60% (0.94-2.38) at both 5% or 20% seroprevalence. ConclusionFor SARS-CoV-2 serology, SIT2 proved to be the best diagnostic choice at both 5% and 20% seroprevalence in all tested scenarios. It is an easy to apply algorithm and can potentially be helpful for the serology of other infectious diseases.
ABSTRACT
Background: In the context of the COVID-19 pandemic, numerous new serological test systems for the detection of anti-SARS-CoV-2 antibodies have become available quickly. However, the clinical performance of many of them is still insufficiently described. Therefore we compared three commercial, CE-marked, SARS-CoV-2 antibody assays side by side. Methods: We included a total of 1,154 specimens from pre-COVID-19 times and 65 samples from COVID-19 patients ([≥]14 days after symptom onset) to evaluate the test performance of SARS-CoV-2 serological assays by Abbott, Roche, and DiaSorin. Results: All three assays presented with high specificities: 99.2% (98.6-99.7) for Abbott, 99.7% (99.2-100.0) for Roche, and 98.3% (97.3-98.9) for DiaSorin. In contrast to the manufacturers specifications, sensitivities only ranged from 83.1% to 89.2%. Although the three methods were in good agreement (Cohens Kappa 0.71-0.87), McNemars test revealed significant differences between results obtained from Roche and DiaSorin. However, at low seroprevalences, the minor differences in specificity resulted in profound discrepancies of positive predictability at 1% seroprevalence: 52.3% (36.2-67.9), 77.6% (52.8-91.5), and 32.6% (23.6-43.1) for Abbott, Roche, and DiaSorin, respectively. Conclusion: We find diagnostically relevant differences in specificities for the anti-SARS-CoV-2 antibody assays by Abbott, Roche, and DiaSorin that have a significant impact on the positive predictability of these tests.
