INFORMATIONAL BOOKLET – SARS – COV2 · The key antigens of SARS-CoV2 along with ACE2 receptor of the human epithelial cell N-Protein S-Protein S2 S1 RBD ACE2 (ACE 2 - The ACE2

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INFORMATIONAL BOOKLET – SARS – COV2

Background

Testing for the novel SARS-CoV2 is primarily via swab-based testing for RNA or testing of blood for antibodies. The most frequently used current test method for RNA is qPCR-based, which identifies the viral nucleic acids when present in sufficient quantity. However, false negative results can be achieved and failure to quarantine the infected patient would be a major setback in containing the viral transmission, which makes a case for doing combined antibody measurement important. Nevertheless, nucleic acid tests are critical in the setting of acute illness, but its accuracy depends on quality and proper collection of the specimen . A combination of two antibody tests, drawn on a patient at least 14 days apart, may be able to measure the presence of active infection. Antibodies have been found to be highly sensitive biomarkers in infectious disease diagnosis.

Previous studies on SARS, MERS and, more recently, those on SARS-CoV2 have shown robust immunological responses in infected individuals. Antibody testing could aid in the diagnosis of COVID19 in combination with qPCR including sub clinical cases. There is insufficient literature to know for certain whether individuals infected with SARS–CoV-2 who produce an antibody response and subsequently recover will be protected either fully or partially from future infection with SARS–CoV-2 or how long protective immunity may last. Recent evidence from a rhesus macaque study does suggest protective immunity after resolution of a primary infection , however, further studies are needed to confirm this.

The value and benefit in testing for RNA viral sample and the antibody testing are summarized in the table below.

Tests for SARS-CoV-2/COVID-19 Potential Users

Type of Test Measure Value Beneficiary

Nucleic amplification test for viral RNA

Antibodydetection

(nasopharyngeal swab, oropharyngeal swab, sputum, bronchoalveolar lavage fluid, others)

Current infection withSARS-CoV-2

Exposure to SARS-CoV-2

Inform individual of infection status so that can anticipate course of illness and take action to prevent transmission)

Inform patient management and actions needed to prevent transmission

Inform actions needed to prevent transmission

Detect susceptible individuals (antibody negative) and those previously infected

Identify individuals with neutralizing antibodies

Facilitate contact tracing and surveillance

Individual

Healthcare or long-term care facility

Public health

Identify those potentially immune to SARS-CoV-2 (if tests can detect protective immunity, individuals could be returned to work

Healthcare facilities: Experimental therapy

Public health

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Preliminary Studies in Antibody Levels of Individuals Infected with SARS-CoV2

Vibrant Antibody Panel – 4 Viral Antigens and 3 Antibody classes – IgM, IgA and IgG

Studies of the 3 subclasses of antibodies in the patient population in China showed that IgM and IgA develop first in individuals and could possibly serve as early markers. The IgG response which is more durable was found even 40 days after infection.

The median duration of IgM and IgA antibody detection were 5 days while IgG was detected in 14 days in most individuals. It is important to note that different individuals will produce variations of these timelines. A better idea of the immune system modulation in an individual can be gauged based on testing them twice or as appropriate to see the production of a stable IgG response.

While the value of antibody tests has been proven with a majority of testing available being able to detect antibodies to a single antigen such as nucleoprotein – the Vibrant Ab Panel is the only one to measure antibody levels against all 4 key antigens of the SARS-CoV-2 as listed below. It is also important to note we will report separately on 3 antibody subclasses – IgM, IgA and IgG-- which can shed light on the broad immune response of the individual. Important highlights to note in our testing are below.

Testing for a single antigen will limit the assay sensitivity as we can see from the individual sensitivities and specificities of antigens listed in our validation document.

It is important to note that studies at Vibrant have been performed using swab positive and negative in the US population and do not rely on external studies.

The antigens were manufactured using the reference genome of SARS-CoV2 that was published and are hence specific to the novel coronavirus SARS-CoV2. Preliminary studies have shown differentiation from antibodies to other coronaviruses, however much larger studies are required to ascertain this which is why the FDA mandates a disclaimer in all antibody tests at this point on potential cross-reactivity.

Testing affected individuals at least twice may help display immune system modulation and also differentiate if the infection is recent vs past.

Vibrant uses chemiluminescence-based detection for all antibody subclasses in addition to a procedure called IgG stripping during detection of IgM, which enhances the sensitivity of our assay.

IgM antibodies to SARS-CoV-2 are generally detectable in blood several days after initial infection, although levels over the course of infection are not well characterized. IgG antibodies to SARS-CoV-2 become detectable later following infection. Positive results for both IgG and IgM could occur after infection and can be indicative of acute or recent infection.

Figure 1. Median duration of antibody responses in SARS-CoV2 individuals against the nucleoprotein


Clinical Performance

Regulatory Statement

Antigens

A combined table with the total sensitivity and specificity is provided below for reference. The complete study of individual marker sensitivities and specificities are in the validation document.

Figure 2. The key antigens of SARS-CoV2 along with ACE2 receptor of the human epithelial cell

N-Protein

S-Protein

S2

S1

RBD

ACE2

(ACE 2 - The ACE2 protein is the cell surface receptor on the human epithelial cells in the respiratory tract to which the Spike proteins of the virus binds to gain access into and multiply using the human cell. This leads to eventual release of virions into the lumen ( inside space of the tubular respiratory tract )

S1 Spike protein - The S1 subunit of the ectodomain mediates binding of the virion to host cell-surface receptors through its receptor-binding domain (RBD)Receptor Binding Domain – Part of the S1 Spike subunit that actually binds to the ACE2 receptor of human epithelial cellS2 Spike protein - The S2 subunit fuses with both host and viral membranes, by undergoing dramatic structural changesNucleoprotein - Packages the positive strand viral genome RNA into a helical ribonucleocapsid (RNP) and plays a fundamental role during virion assembly through its interactions with the viral genome and membrane protein M. Plays an important role in enhancing the efficiency of subgenomic viral RNA transcription as well as viral replication.

Vibrant COVID-19 Ab

OverallIgG/IgA/IgM

Total

Total Analysis(95% Confidence)

Clinical Diagnosis - NP Swab Positive

Positive

Positive 34

34

5

305

39

340

Sensitivity = 97.14%(85.47% - 99.30%)

Specificity = 98.36%(96.22% - 99.30%)1 300 301Negative

Controls

Report from the American Society for Microbiology COVID-19 International Summit, 23 March 2020: Value of Diagnostic Testing for SARS–CoV-2/COVID-19.Robin Patel, Esther Babady, Elitza S. Theel, Gregory A. Storch, Benjamin A. Pinsky, Kirsten St. George, Tara C. Smith, Stefano Bertuzzi mBio Mar 2020, 11 (2) e00722-20; DOI: 10.1128/mBio.00722-20

Reinfection could not occur in SARS-CoV-2 infected rhesus macaques. Linlin Bao, Wei Deng, Hong Gao, Chong Xiao, Jiayi Liu, Jing Xue, Qi Lv, Jiangning Liu, Pin Yu, Yanfeng Xu, Feifei Qi, Yajin Qu, Fengdi Li, Zhiguang Xiang, Haisheng Yu, Shuran Gong, Mingya Liu, Guanpeng Wang, Shunyi Wang, Zhiqi Song, Wenjie Zhao, Yunlin Han, Linna Zhao, Xing Liu, Qiang Wei, Chuan Qin, bioRxiv 2020.03.13.990226; doi: https://doi.org/10.1101/2020.03.13.990226

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This test has been reviewed by the FDA.Negative results do not rule out SARS-CoV-2 infection, particularly in those who have been in contact with the virus. Follow-up testing with a molecular diagnostic should be considered to rule out infection in these individuals.Results from antibody testing should not be used as the sole basis to diagnose or exclude SARS-CoV-2 infection or to inform infection status.Positive results may be due to past or present infection with non-SARS-CoV-2 coronavirus strains, such as coronavirus HKU1, NL63, OC43, or 229E.Not for the screening of donated blood

Documents

INFORMATIONAL BOOKLET – SARS – COV2 · The key antigens of SARS-CoV2 along with ACE2 receptor of the human epithelial cell N-Protein S-Protein S2 S1 RBD ACE2 (ACE 2 - The ACE2