Evaluation of SARS-CoV-2 lateral-flow test with clinical samples
Avacta Group has received the first data for its SARS-CoV-2 rapid antigen test from ongoing clinical studies in Europe and the UK, which show excellent performance in identifying patients with an infectious viral load and no false positive results.
Avacta’s SARS-CoV-2 rapid antigen test has been developed to identify infectious individuals so that they can isolate promptly and reduce the spread of the virus. A recent report from the Liverpool COVID SMART pilot study indicates that infected individuals had a significant chance of infecting their contacts if they had a viral load measured by PCR (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, with a lower Ct value indicating a higher viral load.
Initial evaluation of Avacta’s lateral-flow rapid antigen test with clinical samples has been carried out at two sites, one in the EU and one in the UK, using patient samples with viral loads confirmed by PCR. Thirty positive samples were tested with Ct values ≤26, with half of those in the range 22–26, and the lateral-flow test identified 29/30 of these correctly as positive. This indicates a clinical sensitivity of 96.7% for samples with a Ct value <26.
Importantly, out of a total of 26 negative samples tested with the lateral-flow device, the test correctly identified all as negative, giving a clinical specificity of 100%. High specificity is critical for a lateral-flow test for mass screening so that large numbers of false positives are not generated, which would create a major burden on follow-on testing resources, and result in a significant socio-economic cost of unnecessarily isolating people.