Analysis of seven SARS-CoV-2 rapid antigen tests in detecting omicron (B.1.1.529) versus delta (B.1.617.2) using cell culture supernatants and clinical specimens

Abstract

Purpose Omicron is rapidly spreading as a new SARS-CoV-2 variant of concern (VOC). The question whether this new variant has an impact on SARS-CoV-2 rapid antigen test (RAT) performance is of utmost importance. To obtain an initial estimate regarding differences of RATs in detecting omicron and delta, seven commonly used SARS-CoV-2 RATs from different manufacturers were analysed using cell culture supernatants and clinical specimens. Methods For this purpose, cell culture-expanded omicron and delta preparations were serially diluted in Dulbecco’s modified Eagle’s Medium (DMEM) and the Limit of Detection (LoD) for both VOCs was determined. Additionally, clinical specimens stored in viral transport media or saline (n = 51) were investigated to complement in vitro results with cell culture supernatants. Ct values and RNA concentrations were determined via quantitative reverse transcription polymerase chain reaction (RT-qPCR). Results The in vitro determination of the LoD showed no obvious differences in detection of omicron and delta for the RATs examined. The LoD in this study was at a dilution level of 1:1,000 (corresponding to 3.0—5.6 × 106 RNA copies/mL) for tests I–V and at a dilution level of 1:100 (corresponding to 3.7—4.9 × 107 RNA copies/mL) for tests VI and VII. Based on clinical specimens, no obvious differences were observed between RAT positivity rates when comparing omicron to delta in this study setting. Overall positivity rates varied between manufacturers with 30–81% for omicron and 42–71% for delta. Test VII was only conducted in vitro with cell culture supernatants for feasibility reasons. In the range of Ct < 23, positivity rates were 50–100% for omicron and 67–93% for delta. Conclusion In this study, RATs from various manufacturers were investigated, which displayed no obvious differences in terms of analytical LoD in vitro and RAT positivity rates based on clinical samples comparing the VOCs omicron and delta. However, differences between tests produced by various manufacturers were detected. In terms of clinical samples, a focus of this study was on specimens with high virus concentrations. Further systematic, clinical and laboratory studies utilizing large datasets are urgently needed to confirm reliable performance in terms of sensitivity and specificity for all individual RATs and SARS-CoV-2 variants.

Evaluation of the analytical sensitivity of ACON and LumiraDx SARS-CoV-2 rapid antigen tests using samples with presumed Omicron variant

“…One study found 10-100 fold decreased analytical sensitivity of Ag RDT for detecting Omicron compared to Delta VoC [14] , while another noted significant variability between Ag RDT in ability to detect Omicron VoC [15] . In contrast other studies found only small or no differences in the analytical sensitivity to Omicron compared to previous VoC [16] , [17] , [18] , [19] , [20] . Finally, one study found that 4 AG RDT had increased sensitivity for detection of Omicron compared to Delta VoC [21] .…”

Post-Market Surveillance of Six COVID-19 Point-of-Care Tests Using Pre-Omicron and Omicron SARS-CoV-2 Variants

“…Previous studies evaluating RADTs have consistently reported similar or reduced clinical sensitivity with Omicron as compared to early pandemic variants (21, 37, 39). For example, multiple studies investigating the Abbott Panbio using cultured virus (40) and clinical samples (23, 41) have shown no sensitivity loss against Omicron. Alternatively, work by Bekliz al.…”

SARS‐CoV‐2 nucleocapsid: Biological functions and implication for disease diagnosis and vaccine design

“…The Omicron variant is the latest strain with high transmissibility potential harbouring P13L, R203K, G204R substitutions, and amino acid deletions at positions 31–33 of N protein 67 . Due to these genetic variations, several reports suggested lower sensitivity of diagnostics targeting N protein especially for samples with Ct values >25 (lower viral load) (Table 2), 57,68–70 while some other studies reported similar sensitivities 71–73 . The lower sensitivity of antigen tests for detection of the Omicron variant could be justified by considering the clinical and virological aspects.…”

“…67 Due to these genetic variations, several reports suggested lower sensitivity of diagnostics targeting N protein especially for samples with Ct values >25 (lower viral load) (Table 2), 57,[68][69][70] while some other studies reported similar sensitivities. [71][72][73] The lower sensitivity of antigen tests for detection of the Omicron variant could be justified by considering the clinical and virological aspects. As Cocherie et al reported, lower viral load is observed in Omicron-infected patients compared with Delta-infected patients even at the same stage of disease.…”