Anti-SARS-CoV-2 Antibody Levels Measured by the AdviseDx SARS-CoV-2 Assay Are Concordant with Previously Available Serologic Assays but Are Not Fully Predictive of Sterilizing Immunity

Abstract

With the availability of widespread SARS-CoV-2 vaccination, high-throughput quantitative anti-spike protein serological testing will likely become increasingly important. Here, we investigated the performance characteristics of the recently FDA-authorized semiquantitative anti-spike protein AdviseDx SARS-CoV-2 IgG II assay compared to the FDA-authorized anti-nucleocapsid protein Abbott Architect SARS-CoV-2 IgG, Roche Elecsys anti-SARS-CoV-2-S, EuroImmun anti-SARS-CoV-2 enzyme-linked immunosorbent assay (ELISA), and GenScript surrogate virus neutralization assays and examined the humoral response associated with vaccination, natural protection, and vaccine breakthrough infection. The AdviseDx assay had a clinical sensitivity at 14 days after symptom onset or 10 days after PCR detection of 95.6% (65/68; 95% confidence interval [CI], 87.8 to 98.8%), with two discrepant individuals seroconverting shortly thereafter. The AdviseDx assay demonstrated 100% positive percent agreement with the four other assays examined using the same symptom onset or PCR detection cutoffs. Using a recently available WHO international standard for anti-SARS-CoV-2 antibody, we provide assay unit conversion factors to international units for each of the assays examined. We performed a longitudinal survey of healthy vaccinated individuals, finding that median AdviseDx immunoglobulin levels peaked 7 weeks after first vaccine dose at approximately 4,000 IU/ml. Intriguingly, among the five assays examined, there was no significant difference in antigen binding level or neutralizing activity between two seropositive patients protected against SARS-CoV-2 infection in a previously described fishing vessel outbreak and five health care workers who experienced vaccine breakthrough of SARS-CoV-2 infection, all with variants of concern. These findings suggest that protection against SARS-CoV-2 infection cannot currently be predicted exclusively using in vitro antibody assays against wild-type SARS-CoV-2 spike. Further work is required to establish protective correlates for SARS-CoV-2 infection.

Keywords: Abbott Architect; COVID-19; SARS-CoV-2; anti-SARS-CoV-2; coronavirus; correlates of protection; serology; spike IgG; spike protein; vaccination.

FIG 1

AdviseDx SARS-CoV-2 IgG II values for patients with a PCR-confirmed SARS-CoV-2 infection who were >14 days beyond symptom onset or >10 days beyond the first positive PCR result and control serum collection prior to the SARS-CoV-2 pandemic (A). The dotted line represents the assay positive cutoff (50 AU/ml) set by the manufacturer. Gold squares indicate patients who seroconverted at 13 and 18 days following their first positive PCR result. The purple triangle represents a severely ill COVID-19 patient who died 17 days after symptom onset. One hundred four serum samples obtained prior to the emergence of SARS-CoV-2 were analyzed for assay specificity (B). The median value of these negative controls was 1.8 AU/ml (range, 0 to 32.9). The dotted line represents the positive threshold.

FIG 2

Correlation of AdviseDx SARS-CoV-2 IgG II assays results to the Abbott Architect anti-N (A), Roche anti-S (B), EuroImmun anti-S (C), and GenScript (D) assays. The same specimens were run on all five platforms. AdviseDx and Roche results were log-transformed before performing linear regression. Results demonstrated strong agreement, and goodness of fit (R²) was measured as 0.42, 0.66, 0.73, and 0.74, respectively. Dotted lines represent the manufacturer’s positive cutoff values.

FIG 3

Serial measurements of anti-S IgG levels and surrogate neutralization results in four patients with acute SARS-CoV-2 infection (A) and four patients who received the mRNA-1273 or BNT162b2 SARS-CoV-2 vaccine (B). Increasing anti-S levels and neutralization were observed in all patients as time from exposure increased. Black squares represent anti-S AdviseDx SARS-CoV-2 results, and blue triangles show percent neutralization calculated from the GenScript neutralization assay. At later time points, vaccinated patients had lower anti-S levels with sustained neutralization activity. Curves connected data points were plotted in Prism 9 using the Akima spline.