Salivary SARS-CoV-2 (N) IgG

Intended Use

The Salimetrics® SARS-CoV-2 N-Protein Salivary IgG ELISA kit is an enzyme-linked immunoassay specifically designed and validated for the qualitative measurement of human IgG specific to the SARS-CoV-2 Nucleocapsid protein (N-protein) in oral fluid.

It is intended for surveillance testing and not for diagnostic use. This assay kit was optimized and validated for performance in human oral fluid and has not been validated for other human sample types, such as human serum or plasma.

Surveillance testing for antibodies to the SARS-CoV-2 virus can be used to determine if an individual may have been exposed to or infected with this virus, and can be used to understand the percentage of people within a population or community that have developed antibodies to the virus (known as “surveillance tests,” or sero-surveys). (From the FDA guidance document (https://www.fda.gov/media/137599/download))

• When used for surveillance, the results can help determine how widely the virus has spread in communities and how far the pandemic has progressed. Results from tests used for surveillance only are generally not shared with individual patients and are critical for understanding the extent of and risk factors associated with infection.
• Testing individuals may help identify who has developed antibodies against SARS-CoV-2. The results of ongoing research are needed before it is known whether these antibodies are associated with protection from future infection. Current results can help inform who may qualify to donate blood that can be used to manufacture convalescent plasma.

Please read the complete kit insert before performing this assay. Failure to follow kit procedure and recommendations for saliva collection and sample handling may result in unreliable values.

For further information about this kit, its application, or the procedures in this insert, please contact the technical service team at Salimetrics or your local sales representative.

Introduction

The novel Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) was initially identified in the Winter of 2019 with an outbreak designation soon after, at the end of the year (1, 2). The virus rapidly spread achieving global pandemic status in March 2020 and resulted in widespread containment and confinement public health measures in most countries throughout the world.

In addition to virus exposure, there is an urgent need to better understand the levels and duration of protective immunity for public health considerations. The Salimetrics SARS-CoV-2 N-Protein Salivary IgG ELISA assay meets the technical requirement for high sensitivity and specificity performance, while using a saliva sample, allowing for central testing at scale. The main source of salivary IgG antibodies is serum, so it is not surprising that salivary IgG antibodies directly reflect the specificity and activity of those found in serum (3, 4). Oral fluid is, thus, an easily accessible surrogate to serum or plasma in this regard and enables salivary serology studies, surveillance tests or sero-surveys (5). Testing can help determine who has developed antibodies against SARS-CoV-2. Importantly, we have determined that human IgG withstands conditions commonly used for viral heat inactivation (60° or 65°C for 30 min and 95°C for 5 min). The main utility of antibody tests for SARS-CoV-2 supported by the WHO, CDC, FDA and AMA are surveillance studies and the Salimetrics N-Protein IgG ELISA kit meets this need.

Antibody levels decrease in the serum and saliva of COVID-19 patients over time (6-8), and importantly vary depending on disease severity (9, 10). In fact, a higher number of asymptomatic participants become seronegative at 60 days indicating a true decline over a 2-month period rather than as an artifact of assay performance (6, 7). Therefore, our assay is benchmarked on validated commercial serum kit performance instead of molecular tests. Maximizing the likelihood of antibody detection, N protein was chosen as an advantage since it represents the most immunodominant protein in the coronavirus family.

SALIVARY COVID-19 (SARS-CoV-2) IgG ASSAY PRINCIPLE

This is a salivary serological ELISA kit where viral Nucleocapsid antigen is coated on microtiter plates and human IgG antibodies in test saliva samples are detected using an Anti-Human IgG detection antibody linked to horseradish peroxidase (HRP). After each incubation, unbound components are washed away. The levels of IgG bound to the viral antigen are measured by the reaction of the HRP enzyme to the substrate tetramethylbenzidine (TMB). This reaction produces a blue color. A yellow color is formed after stopping the reaction with an acidic solution. The Optical Density is read on a standard plate reader at 450 nm. The total amount of anti-IgG HRP Enzyme Conjugate detected is proportional to the amount of anti-SARS-CoV-2 IgG present in the sample. Normalized Arbitrary Units are calculated by dividing the sample Signal Optical Density by the total IgG concentration of the same sample, determined using the Salimetrics total IgG assay kit, and multiplying this value by 100. The Normalized Arbitrary Units are used to determine if an individual has been infected at least 14 days prior to testing where values above 1.2 are considered positive and below 0.8 negative. Samples reading between these values are considered borderline and a repeat test is recommended for these samples and/or a second collection one or two weeks later.