Current immunoassays and detection of antibodies elicited by Omicron SARS‐CoV‐2 infection

Abstract

The present study aimed to determine whether current commercial immunoassays are adequate for detecting anti‐Omicron antibodies. We analyzed the anti‐SARS‐CoV‐2 antibody response of 23 unvaccinated individuals 1–2 months after an Omicron infection. All blood samples were tested with a live virus neutralization assay using a clinical Omicron BA.1 strain and four commercial SARS‐CoV‐2 immunoassays. We assessed three anti‐Spike immunoassays (SARS‐CoV‐2 IgG II Quant [Abbott S], Wantaï anti‐SARS‐CoV‐2 antibody ELISA [Wantaï], Elecsys Anti‐SARS‐CoV‐2 S assay [Roche]) and one anti‐Nucleocapsid immunoassay (Abbott SARS‐CoV‐2 IgG assay [Abbott N]). Omicron neutralizing antibodies were detected in all samples with the live virus neutralization assay. The detection rate of the Abbott S, Wantai, Roche, and Abbott N immunoassays were 65.2%, 69.6%, 86.9%, and 91.3%, respectively. The sensitivities of Abbott S and Wantai immunoassays were significantly lower than that of the live virus neutralization assay (p = 0.004, p = 0.009; Fisher's exact test). Antibody concentrations obtained with anti‐S immunoassays were correlated with Omicron neutralizing antibody concentrations. These data provide clinical evidence of the loss of performance of some commercial immunoassays to detect antibodies elicited by Omicron infections. It highlights the need to optimize these assays by adapting antigens to the circulating SARS‐CoV‐2 strains.

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“…ELISA total values are expressed in BAU/mL, and with an assigned cutoff at 7.14 BAU/mL, as previously described [ 19 , 20 ]. The SARS-CoV-2 IgG assay (Abbott Nuc) was used to detect anti-Nuc antibodies using a threshold fixed at 1.4 [ 21 ].…”

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“…Commercial assays developed early during the pandemic are based on ancestral/wild-type antigens. Subsequently, there is potential for differential performance in the Omicron-era: in particular, S-and RBD-specific immunoassays have shown significantly reduced performance (112)(113)(114), and decreased comparability of quantitative results (115).…”