The U.S. FDA has granted emergency use authorization (EUA) to Quanterix Corp.’s SARS-CoV-2 IgG antibody test, which tests blood samples for evidence of recent or prior COVID-19 infection. The test could also be used to measure antibody response to a COVID-19 vaccine.

The Simoa Semi-Quantitative SARS-CoV-2 IgG antibody test is indicated for the qualitative and semi-quantitative detection of IgG antibodies to SARS-CoV-2 in human serum and dipotassium EDTA plasma from a venous blood draw. Under the terms of the EUA, the test must be run in CLIA laboratories that meet the requirements to perform moderate or high complexity tests, and samples should be tested at least 15 days after the onset of symptoms.

The test, which uses the company’s Simoa single molecule array technology, is run on Quanterix’s Simoa HD-X Analyzer, an automated high-throughput immunoassay instrument.

While many SARS-CoV-2 antibody tests have received an EUA from the FDA, the Quanterix assay is one of only a few tests that offer semi-quantitative results, allowing clinicians to see the antibody level, rather than just whether antibodies are present. The assay provides a numerical result showing concentration of antibodies from 0.21 to 250 µg/mL.

The semi-quantitative result makes the assay a potential tool for assessing the durability of vaccine response, explained Quanterix CEO Kevin Hrusovsky.

“There are so many questions that haven’t been answered around how durable are these antibodies opposite the vaccine,” Hrusovsky told BioWorld. “So, the amount of the antibody, we think can be pretty important.”

The Billerica, Mass.-based company plans an initial marketing push to vaccine producers and companies focused on development of COVID-19 treatments, such as convalescent plasma therapies.

Simoa technology

The Simoa antibody assay uses an automated paramagnetic microbead based immunoassay to detect antibodies directed against the novel coronavirus’s spike protein. Since currently authorized COVID-19 vaccines, as well as those in development, are designed to elicit an antibody response in the spike protein, the Simoa assay could be useful in measuring the antibody response in individuals who have received a vaccine, according to the company.

In validation testing, the assay demonstrated a 100% positive percent agreement (sensitivity) and a 99.2% negative agreement (specificity) in clinical samples 15 or more days following a positive result with a PCR test.

The Simoa technology is also being used in other facets of COVID-19 research, including as an antigen test, which measures the viral load of SARS-CoV-2.

In October 2020, Quanterix received a $18.2 million contract with the National Institutes of Health to accelerate development of its antigen test using the ultra-sensitive Simoa technology. The contract is part of the NIH Rapid Acceleration of Diagnostics (RADx) initiative and supports assay kit manufacturing capacity and commercial deployment.

Preliminary results with the antigen assay indicate that it detects the SARS-CoV-2 virus in a variety of sample types, including self-collected capillary blood, saliva and nasal swabs.

“We have submitted the initial phase of an EUA on that antigen test,” Hrusovsky said. “The evidence would suggest we can see this antigen in blood, which is very unique. There haven’t been any tests approved at this point that see the antigen in blood.”

The Simoa technology is also showing promise in research to help predict which patients will experience severe forms of COVID-19, both in the acute phase and over the long-term.

Quantitative testing using serum neurofilament light chair (sNfL) as a biomarker for neuronal injury showed that COVID-19 status was significantly linked with sNfL, suggesting acute or chronic neuro-axonal damage from COVID-19. These findings were published in the Journal of Neurology.

The Simoa technology is also being used to profile the innate immune response in COVID-19 patients by measuring cytokines in the blood. Research published in Science suggests that a reduction of interferon type I in the blood could help detect which patients are at risk for dysregulation of the inflammatory response and a “cytokine storm.”