Automated antigen assays display a high heterogeneity for the detection of SARS-CoV-2 variants of concern, including several Omicron sublineages.
Andreas Osterman, Franziska Krenn, Maximilian Iglhaut, Irina Badell, Andreas Lehner, Patricia M Sp��th, Marcel Stern, Hanna Both, Sabine Bender, Maximilian Muenchhoff, Alexander Graf, Stefan Krebs, Helmut Blum, Timo Grimmer, J��rgen Durner, Ludwig Czibere, Christopher D��chert, Natascha Grzimek-Koschewa, Ulrike Protzer, Lars Kaderali, Hanna-Mari Baldauf, Oliver T Keppler
Author Information
Andreas Osterman: Max von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU M��nchen, Munich, Germany.
Franziska Krenn: Max von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU M��nchen, Munich, Germany.
Maximilian Iglhaut: Max von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU M��nchen, Munich, Germany.
Irina Badell: Max von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU M��nchen, Munich, Germany.
Andreas Lehner: Max von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU M��nchen, Munich, Germany.
Patricia M Sp��th: Max von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU M��nchen, Munich, Germany.
Marcel Stern: Max von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU M��nchen, Munich, Germany.
Hanna Both: Max von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU M��nchen, Munich, Germany.
Sabine Bender: Max von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU M��nchen, Munich, Germany.
Maximilian Muenchhoff: Max von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU M��nchen, Munich, Germany.
Alexander Graf: Laboratory for Functional Genome Analysis, Gene Center, LMU M��nchen, Munich, Germany.
Stefan Krebs: Laboratory for Functional Genome Analysis, Gene Center, LMU M��nchen, Munich, Germany.
Helmut Blum: Laboratory for Functional Genome Analysis, Gene Center, LMU M��nchen, Munich, Germany.
Timo Grimmer: Department of Psychiatry and Psychotherapy, Klinikum Rechts der Isar, School of Medicine, Technical University of Munich, Munich, Germany.
Ludwig Czibere: Labor Becker MVZ GbR, Munich, Germany.
Christopher D��chert: Max von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU M��nchen, Munich, Germany.
Natascha Grzimek-Koschewa: Max von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU M��nchen, Munich, Germany.
Ulrike Protzer: German Center for Infection Research (DZIF), Partner Site, Munich, Germany.
Lars Kaderali: Institute of Bioinformatics, University Medicine Greifswald, Greifswald, Germany.
Hanna-Mari Baldauf: Max von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU M��nchen, Munich, Germany. baldauf@mvp.lmu.de.
Oliver T Keppler: Max von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU M��nchen, Munich, Germany. keppler@mvp.lmu.de. ORCID
Diagnostic tests for direct pathogen detection have been instrumental to contain the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) pandemic. Automated, quantitative, laboratory-based nucleocapsid antigen (Ag) tests for SARS-CoV-2 have been launched alongside nucleic acid-based test systems and point-of-care (POC) lateral-flow Ag tests. Here, we evaluated four commercial Ag tests on automated platforms for the detection of different sublineages of the SARS-CoV-2 Omicron variant of concern (VoC) (B.1.1.529) in comparison with "non-Omicron" VoCs. A total of 203 Omicron PCR-positive respiratory swabs (53 BA.1, 48 BA.2, 23 BQ.1, 39 XBB.1.5 and 40 other subvariants) from the period February to March 2022 and from March 2023 were examined. In addition, tissue culture-expanded clinical isolates of Delta (B.1.617.2), Omicron-BA.1, -BF.7, -BN.1 and -BQ.1 were studied. These results were compared to previously reported data from 107 clinical "non-Omicron" samples from the end of the second pandemic wave (February to March 2021) as well as cell culture-derived samples of wildtype (wt) EU-1 (B.1.177), Alpha VoC (B.1.1.7) and Beta VoC (B.1.351)). All four commercial Ag tests were able to detect at least 90.9% of Omicron-containing samples with high viral loads (Ct���<���25). The rates of true-positive test results for BA.1/BA.2-positive samples with intermediate viral loads (Ct 25-30) ranged between 6.7% and 100.0%, while they dropped to 0 to 15.4% for samples with low Ct values (>���30). This heterogeneity was reflected also by the tests' 50%-limit of detection (LoD50) values ranging from 44,444 to 1,866,900 Geq/ml. Respiratory samples containing Omicron-BQ.1/XBB.1.5 or other Omicron subvariants that emerged in 2023 were detected with enormous heterogeneity (0 to 100%) for the intermediate and low viral load ranges with LoD50 values between 23,019 and 1,152,048 Geq/ml. In contrast, detection of "non-Omicron" samples was more sensitive, scoring positive in 35 to 100% for the intermediate and 1.3 to 32.9% of cases for the low viral loads, respectively, corresponding to LoD50 values ranging from 6181 to 749,792 Geq/ml. All four assays detected cell culture-expanded VoCs Alpha, Beta, Delta and Omicron subvariants carrying up to six amino acid mutations in the nucleocapsid protein with sensitivities comparable to the non-VoC EU-1. Overall, automated quantitative SARS-CoV-2 Ag assays are not more sensitive than standard rapid antigen tests used in POC settings and show a high heterogeneity in performance for VoC recognition. The best of these automated Ag tests may have the potential to complement nucleic acid-based assays for SARS-CoV-2 diagnostics in settings not primarily focused on the protection of vulnerable groups. In light of the constant emergence of new Omicron subvariants and recombinants, most recently the XBB lineage, these tests' performance must be regularly re-evaluated, especially when new VoCs carry mutations in the nucleocapsid protein or immunological and clinical parameters change.
