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. 2023 Oct 24;61(10):e0013823.
doi: 10.1128/jcm.00138-23. Epub 2023 Sep 20.

Sensitivity of rapid antigen tests against SARS-CoV-2 Omicron and Delta variants

Anuradha Rao #  1   2 , Adrianna Westbrook #  1   2 , Leda Bassit  1   3 , Richard Parsons  1   4 , Eric Fitts  5 , Morgan Greenleaf  1   6 , Kaleb McLendon  1   5   7 , Julie A Sullivan  1   2 , William O'Sick  1   5   7 , Tyler Baugh  1   5   7 , Heather B Bowers  1   3 , Filipp Frank  8 , Ethan Wang  9 , Mimi Le  2 , Jennifer Frediani  1   4 , Pavitra Roychoudhury  10 , Alexander L Greninger  10 , Robert Jerris  11 , Nira R Pollock  12 , Eric A Ortlund  1   8 , John D Roback  1   5   7 , Wilbur A Lam  1   2   13   14 , Anne Piantadosi  5   9
Affiliations

Sensitivity of rapid antigen tests against SARS-CoV-2 Omicron and Delta variants

Anuradha Rao et al. J Clin Microbiol. .

Abstract

Rapid antigen tests (RATs) have become an invaluable tool for combating the COVID-19 pandemic. However, concerns have been raised regarding the ability of existing RATs to effectively detect emerging SARS-CoV-2 variants. We compared the performance of 10 commercially available, emergency use authorized RATs against the Delta and Omicron SARS-CoV-2 variants using both individual patient and serially diluted pooled clinical samples. The RATs exhibited lower sensitivity for Omicron samples when using PCR cycle threshold (CT) value (a rough proxy for RNA concentration) as the comparator. Interestingly, however, they exhibited similar sensitivity for Omicron and Delta samples when using quantitative antigen concentration as the comparator. We further found that the Omicron samples had lower ratios of antigen to RNA, which offers a potential explanation for the apparent lower sensitivity of RATs for that variant when using C T value as a reference. Our findings underscore the complexity in assessing RAT performance against emerging variants and highlight the need for ongoing evaluation in the face of changing population immunity and virus evolution.

Keywords: SARS-CoV-2; rapid antigen test.

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Conflict of interest statement

A.L.G. reports contract testing from Abbott, Cepheid, Novavax, Pfizer, Janssen, and Hologic, and research support from Gilead and Merck, outside of the described work. The other authors have declared that no conflict of interest exists.

Figures

Fig 1
Fig 1
Results of testing 10 commercially available rapid antigen tests (RATs) against remnant clinical sample (RCSs) pools. Each of 10 commercially available RATs was tested using sequence-confirmed, serially diluted, and quantified (N2 CT CDC Assay and Quanterix Simoa SARS-CoV-2 N Protein Antigen Test) pools generated from RCSs of the same variant. RCS pool dilutions were tested in replicate, and the Minimum Protein Detected (A) and Maximum N2 C T Detected (B) were defined as the lowest and highest values at which 100% of the replicates were positive, respectively. Panels (A and B) show each RAT’s threshold, represented by an orange (Delta) or black (Omicron) filled circle. Each dot reflects one set of replicates, and when testing was repeated with an independent RCS pool, or an independent lot of tests, results are presented as separate dots. Full results from each experiment are shown in Fig. S1.
Fig 2
Fig 2
Results of testing two commercially available rapid antigen tests against individual remnant clinical samples for Delta (A and B) and Omicron (C and D). Sequence-verified residual mid turbinate samples from 75 individuals with Delta infection and 84 individuals with BA.1 infection underwent RT-PCR testing using the Xpert Xpress CoV-2/Flu/RSV plus & Xpert Xpress SARS-CoV-2 assays (Cepheid), protein quantification using the Simoa SARS-CoV-2 N Protein Antigen assay (Quanterix), and rapid antigen testing (QuickVue or Binax) according to the manufacturer’s instructions. Y-axes reflect natural log(n + 1) transformed antigen concentration. Abbreviations: Cycle threshold (CT).
Fig 3
Fig 3
Correlation between antigen concentration and C T value for individual remnant clinical samples. Sequence-verified residual mid turbinate samples from 163 individuals with Delta infection and 169 individuals with BA.1 infection underwent RT-PCR testing using the Xpert Xpress CoV-2/Flu/RSV plus & Xpert Xpress SARS-CoV-2 assays (Cepheid) and protein testing using the Simoa SARS-CoV-2 N Protein Antigen assay (Quanterix), according to the manufacturer’s instructions. Y-axes reflect natural log(n + 1) transformed antigen concentration. The red circle signifies 41 Delta samples whose C T values were above the assay detection limit and antigen concentrations were below the assay detection limit. Abbreviations: Cycle threshold (C T ).
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