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
Authors: Jungnick Sabrina , Hobmaier Bernhard , Paravinja Natali , Mautner Lena , Hoyos Mona , Konrad Regina , Haase Maren , Baiker Armin , Eberle Ute , Bichler Magdalena , Treis Bianca , Okeyo Mercy , Streibl Barbara , Wimmer Clara , Hepner Sabrina , Sprenger Annika , Berger Carola , Weise Laura , Dangel Alexandra , Ippisch Siegfried , Jonas Walter , Wildner Manfred , Liebl Bernhard , Ackermann Nikolaus , Sing Andreas , Fingerle Volker ,   the Bavarian SARS-CoV-2-Public Health Laboratory Team, Balakin Vadim , Bartha-Dima Bernadett , Bengs Katja , Berger Anja , Boll Kerstin , Carl Anja , Christian Jürgen , Drdlicek Juliana , Eisenberger David , Flechsler Jennifer , Gerdes Lars , Githure George , Govindaswamy Janani , Hupfer Christine , Lutmayr Johannes , Margos Gabriele , Müller Roswitha , Nickel Silke , Pavlovic Melanie , Pecoraro Sven , Reichwald Daniel , Rollins Robert Ethan , Sahm Isabel , Schauer Melanie , Schmidt Sandra , Schulze Gesine , Schülein Anika , Schürmann Eva-Maria , Scuda Nelly , Seebach Judith , Singer Stefanie , Stellberger Thorsten , Tuschak Christian , Zimmermann Pia 
Published: May 2022

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.