Avacta: Rapid COVID-19 antigen test shows ‘very good sensitivity’ and generates ‘no false positive’ results
The test has been developed to identify infectious individuals so that they can isolate promptly and reduce the spread of COVID-19.
High specificity is critical for a lateral flow assay (LFA) test for mass screening so that large numbers of false positives are not generated as this creates a major burden on follow-on testing resources, and results in a significant socio-economic cost of isolating people, unnecessarily, said the company.
“Avacta’s Affimer technology, which is used in the LFA test, is highly specific to the SARS-CoV-2 spike protein, which leads to fewer false positives,” David Wilson, commercial director, diagnostics, Avacta, told BioPharma-Reporter.
The company is now progressing to a full clinical validation with a larger number of patient samples to CE mark the test for professional use, aiming to bring the test to market in Europe around the end of the first quarter of this year.
Viral load
The Liverpool Covid SMART Pilot Study report indicates that individuals with COVID-19 infection have a significant chance of infecting their contacts if they had a viral load measured by PCR, called the cycle threshold value (Ct value), of approximately 25 or lower. The Ct value indicates how many PCR cycles are required to amplify the viral RNA so that it can be detected and a lower Ct value indicates a higher viral load.
Avacta CEO, Alastair Smith, noted the trial data show the company's rapid antigen test shows very good sensitivity in the infectious range of viral loads including at the lower infectious loads with Ct values of 23-26. "This compares very favorably with the data reported in the Liverpool Covid SMART Pilot Study report,” he said.
Outcome of clinical studies
The company said the initial evaluation of its rapid antigen test with clinical samples was carried out at two sites, one in EU and one in the UK using patient samples with viral loads confirmed by PCR.
Thirty positive samples were tested with Ct values of 26 and below, with half of those in the range 22-26, and the lateral flow test identified 29/30 of these correctly as positive, said the developer. “This indicates a clinical sensitivity of 96.7% for samples with a Ct value below 26. Importantly, out of a total of 26 negative samples tested with the lateral flow device, the test correctly identified all 26 as negative, giving a clinical specificity of 100%.”
Point of care testing
Whereas PCR tests require specialized laboratories to obtain results, rapid LFA-based antigen tests allow point-of-care (POC) testing for effective mass-monitoring and disease management by enabling rapid detection of the virus without the need to access to specialized laboratory equipment, said Wilson.
“Mass population testing at/near point of care can provide a result in minutes, rather than 24 hours or more for PCR results, meaning decisions on quarantining can be made immediately where necessary.”
Can this test identify as infectious people who show no signs of the disease, but do in fact carry the coronavirus?
“LFA can test for patients that aren’t showing symptoms but are highly contagious. LFA detects the coronavirus antigen that is produced when a person is infectious, even if they’re not displaying any symptoms. Rapid identification of asymptomatic individuals allows faster quarantine implementation to prevent further spread. This helps to bring the R rate down by helping infectious individuals enter isolation sooner. The test is intended as a large-scale population screening tool, to help prevent the spread of the virus and help with returning to work safely," commented the commerical director.
Dealing with the challenge of COVID-19 variants
Avacta is also doing work to demonstrate that the test detects the new COVID-19 variants, said Wilson.
“Given the team’s understanding of what the mutations are in those new variants and where they are, Avacta thinks it is unlikely that they will present a problem for the test.”
