Elecsys® Anti-SARS-CoV-2 S

Immunoassay for the qualitative and semi-quantitative determination of antibodies to the SARS-CoV-2 spike protein. For use under the Emergency Use Authorization (EUA) only.

Elecsys pack
Immunoassay for the semi-quantitative determination of antibodies to the SARS-CoV-2 spike protein

Elecsys® Anti‑SARS‑CoV‑2 S for use on the cobas e analyzers is an electrochemiluminescence immunoassay intended for qualitative and semi-quantitative detection of antibodies to SARS‑CoV‑2 spike (S) protein receptor binding domain (RBD) in human serum and plasma (lithium heparin, dipotassium-EDTA, tripotassium-EDTA, and sodium citrate). The Elecsys Anti‑SARS‑CoV‑2 S assay is intended as an aid in identifying individuals with an adaptive immune response to SARS‑CoV‑2, indicating recent or prior infection. The Elecsys Anti‑SARS‑CoV‑2 S assay should not be used to diagnose or exclude acute SARS‑CoV‑2 infection.

SARS-CoV-2: An overview of virus structure, transmission and detection

SARS-CoV-2, the causative agent of Coronavirus Disease 2019 (COVID-19), is an enveloped, single-stranded RNA Betacoronavirus. Seven coronaviruses have been identified as agents of human infection, causing disease ranging from mild common cold to severe respiratory failure.1

SARS-CoV-2 is transmitted primarily from person-to-person through respiratory droplets and aerosols.2,3 The incubation period from infection to detectable viral load in the host commonly ranges from two to 14 days.4,5 Detection of viral load can be associated with the onset of clinical signs and symptoms, although a considerable proportion of individuals remain asymptomatic or mildly symptomatic.6-8 The interval during which an individual with COVID-19 is infectious has not yet been clearly established, however, transmission from symptomatic, asymptomatic, and pre-symptomatic individuals has been well described.9-11


Coronavirus genomes encode 4 main structural proteins: spike (S), envelope (E), membrane (M), and nucleocapsid (N). The S protein is a very large transmembrane protein that assembles into trimers to form the distinctive surface spikes of coronaviruses. Each S monomer consists of an N-terminal S1 subunit and a membrane-proximal S2 subunit. The virus gains entry to the host cell through binding of the S protein to the angiotensin-converting enzyme 2 (ACE2) receptor, which is present on the surface of numerous cell types including the alveolar type II cells of the lung and epithelial cells of the oral mucosa.12,13 Mechanistically, ACE2 is engaged by the receptor-binding domain (RBD) on the S1 subunit.14,15

Upon infection with SARS-CoV-2, the host usually mounts an immune response against the virus, typically including production of specific antibodies against viral antigens. IgM and IgG antibodies against SARS-CoV-2 appear to arise nearly simultaneously in blood.16 There is significant inter-individual difference in the levels and chronological appearance of antibodies in COVID-19 patients, but median seroconversion has been observed at approximately two weeks.17-20

After infection or vaccination, the binding strength of antibodies to antigens increases over time - a process called affinity maturation21. High‑affinity antibodies can elicit neutralization by recognizing and binding specific viral epitopes22,23. Antibodies against SARS‑CoV‑2 with strong neutralizing capacity, especially potent if directed against the RBD, have been identified.24-27 Numerous vaccines for COVID-19 are in development, many of which focus on eliciting an immune response to the RBD.28-30

Structure of the SARS-CoV-2 spike protein and binding to host receptor

Illustration of the structure of the spike protein

Positive Percent Agreement

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Positive Percent Agreement

A total of 1485 samples from 331 symptomatic patients (including 172 samples from 172 hospitalized patients) with a PCR confirmed SARS‑CoV‑2 infection were tested with the Elecsys Anti‑SARS‑CoV‑2 S assay. 1 or more sequential samples from these patients were collected at various time points after PCR confirmation. Positive percent agreement (PPA) was correlated with days post PCR specimen collection, and the results are shown for the first bleed per time bin.

First bleed

233 of the tested samples had a sampling date of 15 days or later after diagnosis with PCR. 225 of these 233 samples were determined with ≥ 0.8 U/mL in the Elecsys Anti‑SARS‑CoV‑2 S assay and hence considered positive, resulting in a PPA of 96.6 % (95 % CI: 93.35‑98.51 %) in this sample cohort.


Days after PCR positive result Number tested Pos Neg PPA (%) 95 % CI* (%)
0-7 32 29 3 90.6 (74.9 - 98.0)
8-14 77 67 10 87.0 (77.4 - 93.5)
≥ 15 233 225 8 96.6 (93.3 - 98.5)
* = confidence interval

Analytical specificity 31

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Analytical specificity 31

A total of 1,468 potentially cross-reactive samples collected before October 2019, including anti-MERS-CoV positive samples, samples from individuals with common cold symptoms, and samples from individuals confirmed to be infected with one of the four common cold coronaviruses were tested with the Elecsys® Anti-SARS-CoV-2 S assay. Overall specificity in this cohort of potentially cross-reactive samples was 100 % (95 % CI: 99.7 – 100 %).

Cohort N Reactive Specificity (95% CI)
MERS-CoV* 51 0 100 %
Common cold panel** 21 0 100 %
Common Coronavirus panel*** 151 0 100 %
Other potentially cross-reactive samples****   978 0 100 %
Overall 1,468   0 100 %  
* positive for IgG antibodies against the Middle East respiratory syndrome-related coronavirus (MERS-CoV) spike protein subunit S1
** 40 samples from individuals with common cold symptoms, collected before October 2019
*** from individuals with past infection with coronavirus HKU1, NL63, 229E, or OC43, confirmed by antigen testing
**** pre-pandemic samples with reactivity for various other indications, which could have an elevated potential for unspecific interference

Negative Percent Agreement 31

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Negative Percent Agreement 31

A total of 5,991 samples from diagnostic routine and blood donors drawn before October 2019 were tested with the Elecsys® Anti-SARSCoV-2 S assay. Overall Negative Percent Agreement (NPA) in this cohort of pre-pandemic samples was 99.98 % (95 % CI: 99.91 – 100 %).

Cohort N Reactive NPA (95 % CI)
Diagnostic routine  2,528  0 100 % (99.8 – 100 %)
US blood donors 2,713 1 99.9 % (99.7 – 100 %)
African blood donors 750 0 100 % (99.5 – 100 %)
Overall 5,991 1 99.9 % (99.9 – 100 %) 






Estimated course of markers in SARS-CoV-2 infection33


For use under Emergency Use Authorization only. This test has not been FDA-cleared or ‑approved; this test has been authorized by FDA under an Emergency Use Authorization (EUA) for use by authorized laboratories; by laboratories certified under the Clinical Laboratory Improvement Amendments of 1988 (CLIA), 42 U.S.C. 263a, that meet requirements to perform high complexity tests. This test has been authorized only for detecting antibodies against SARS‑CoV‑2, not for any other viruses or pathogens. This test is only authorized for the duration of the declaration that circumstances exist justifying the authorization of emergency use of in vitro diagnostic tests for detection and/or diagnosis of COVID‑19 under Section 564(b)(1) of the Federal Food, Drug, and Cosmetic Act, 21 U.S.C § 360bbb‑3(b)(1), unless the authorization is terminated or revoked sooner.



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System specifications

  • Testing time

    18 minutes

  • Test principle

    One-step double antigen sandwich assay

  • Traceability

    Internal Roche standard for anti-SARS-CoV-2-S consisting of monoclonal antibodies. 1 nM of these antibodies correspond to 20 U/mL of the Elecsys® Anti-SARS-CoV-2 S assay

  • Linear range

    0.4 to 250 U/mL

  • Calibration

    2-point (separate CalSet)

  • Interpretation

    <0.8 U/mL = negative, ≥0.8 U/mL = positive

  • Specimen types

    Serum collected using standard sampling tubes; Li-heparin, K2-EDTA-, K3-EDTA-, and sodium citrate plasma

  • Sample volume

    20 μL cobas e 411 analyzer, cobas e 601 / cobas e 602 modules
    12 μL cobas e 801 module

  • Onboard stability

    cobas e 411/601/602: 28 days
    cobas e 801: 16 weeks

  • Intermediate precision in positive samples

    cobas e 411 analyzer: CV* 1.9 – 2.9 %
    cobas e 601 / cobas e 602 modules: CV 2.7 – 3.6 
    cobas e 801 module: CV 1.4 – 2.4 %