Evaluation of the DiaSorin LIAISON SARS-CoV-2 antigen assay on nasopharyngeal swabs in two different SARS-CoV-2 pandemic waves in Switzerland: The impact of the Omicron variant on its performance.

Background: SARS-CoV-2 antigen tests reliably detect individuals with high viral loads and provide an efficient diagnostic tool to manage the current SARS-CoV-2 pandemic However, mutations in SARS-CoV-2 variants of concerns that appeared after validation of most antigen tests might impact their diagnostic performance.

Objectives: To assess the impact of the Omicron variant on the performance of the DiaSorin LIAISON SARS-CoV-2 antigen test, we evaluated its sensitivity and specificity on nasopharyngeal swabs (NPS) compared to rRT-PCR in the second and the Omicron pandemic wave in Switzerland.

Study Design: A random selection of NPS from patients undergoing SARS-CoV-2 diagnostics by rRT-PCR were collected during the second and the Omicron pandemic wave and further analyzed by the LIAISON antigen test. Sensitivity and specificity compared to rRT-PCR were calculated.

Results: Test performance did not change in the two investigated periods. The overall sensitivity of 75.8% in the second and 76.5% in the Omicron wave increased to 87.1% and 88.4%, excluding samples with rRT-PCR Ct-value >30. By lowering the cut-off from 200 TCID/ml to 62 TCID/ml to discriminate between negative and positive samples using a ROC-curve, the sensitivity resulted in 88.8% for the second and 93.3% for the Omicron pandemic wave. The specificity of the LIAISON antigen test was 100% in both collectives.

Conclusion: Omicron variant does not seem to affect the performance of the LIAISON antigen test. The WHO recommended sensitivity of ≥80% for antigen testing was fulfilled during both pandemic periods in samples with Ct-value <30 or by optimizing the assay cut-off.