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.

Figures

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.