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Review 1: "Sensitivity of SARS-CoV-2 antigen-detecting rapid tests for Omicron variant"

This preprint evaluates the sensitivity of various antigen-based COVID-19 diagnostic kits and found variable sensitivity for patients infected with the Omicron variant-of-concern. Reviewers deemed this study potentially informative, pointing out limitations with frozen samples.

Published onMar 03, 2022
Review 1: "Sensitivity of SARS-CoV-2 antigen-detecting rapid tests for Omicron variant"
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key-enterThis Pub is a Review of
Sensitivity of SARS-CoV-2 antigen-detecting rapid tests for Omicron variant
Description

AbstractBackgroundThe emergence of each novel SARS-CoV-2 variants of concern (VOCs) requires investigation of its potential impact on the performance of diagnostic tests in use, including Antigen-detecting rapid diagnostic tests (Ag-RDT). Although anecdotal reports have been circulating that the newly emerged Omicron variant is in principle detectable by Ag-RDTs, few data on sensitivity are available.MethodsWe have performed 1) analytical sensitivity testing with cultured virus in eight Ag-RDTs and 2) retrospective testing in duplicates with clinical samples from vaccinated individuals with Omicron (n=18) or Delta (n=17) breakthrough infection on seven Ag-RDTs.FindingsOverall, we have found large heterogenicity between Ag-RDTs for detecting Omicron. When using cultured virus, we observed a trend towards lower sensitivity for Omicron detection compared to earlier circulating SARS-CoV-2 and the other VOCs. When comparing performance for Delta and Omicron in a comparable set of clinical samples in seven Ag-RDTs, 124/252 (49.2%) of all test performed showed a positive result for Omicron compared to 156/238 (65.6%) for Delta samples. Sensitivity for both Omicron and Delta between Ag-RDTs was highly variable. Four out of seven Ag-RDTs showed significantly lower sensitivity (p<0.001) to detect Omicron when compared to Delta while three had comparable sensitivity to Delta.InterpretationSensitivity for detecting Omicron is highly variable between Ag-RDTs, necessitating a careful consideration when using these tests to guide infection prevention measures. While analytical and retrospective testing may be a proxy and timely solution to generate performance data, it is not a replacement for clinical evaluations which are urgently needed. Biological and technical reasons for detection failure by some Ag-RDTs need to be further investigated.FundingThis work was supported by the Swiss National Science Foundation (grant numbers 196383, 196644 and 198412), the Fondation Ancrage Bienfaisance du Groupe Pictet, the Fondation Privée des Hôpiteaux Universitaires de Genève and FIND, the global alliance for diagnostics.

RR:C19 Evidence Scale rating by reviewer:

  • Potentially informative. The main claims made are not strongly justified by the methods and data, but may yield some insight. The results and conclusions of the study may resemble those from the hypothetical ideal study, but there is substantial room for doubt. Decision-makers should consider this evidence only with a thorough understanding of its weaknesses, alongside other evidence and theory. Decision-makers should not consider this actionable, unless the weaknesses are clearly understood and there is other theory and evidence to further support it.

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Review:


This is a useful, albeit small, study using patient-derived and lab-cultured samples with various limitations, as explained by the authors.

The sensitivities of the various Ag tests seem about right for Delta/Omicron - and most (if not all) of these were designed for earlier versions of SARS-COV-2.

It would be useful if the authors could add a table summarising the production history/mechanisms of these Ag tests: when they were produced, against which SARS-CoV-2 variant as well as the signaling systems used for detection (their conjugate/substrate) - as these may also account for large differences in their test sensitivities.

The use of archived frozen (freeze-thawed) samples collected in VTM versus fresh samples where only the Ag kit buffers were used in testing likely affected the test sensitivities. However, this is an unavoidable limitation of such retrospective studies.

The statistics and discussion of the limitations by the authors seem reasonable. However, although mostly relevant, the discussion seems quite lengthy and could be more succinct.

Finally, the following sentence seems to be missing a delta variant reference at the end of it:

“When assessing overall test positivity, for Omicron 124/252 (49.2%) of tests showed a positive result compared to 156/238 (65.5%) (z = -3.65, p<.001).”

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