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Updated: Oct 3, 2025
A Rapid, Multiplex Dual Reporter IgG and IgM SARS-CoV-2 Neutralization Assay for a Multiplexed Bead-Based Flow Analysis System
Published on: April 6, 2021
Impaired detection of omicron by SARS-CoV-2 rapid antigen tests
Andreas Osterman1, Irina Badell1, Elif Basara1
1Max Von Pettenkofer Institute and Gene Center, Virology, National Reference Center for Retroviruses, LMU München, Feodor-Lynen-Str. 23, 81377, Munich, Germany.
Abstract:
Since autumn 2020, rapid antigen tests (RATs) have been implemented in several countries as an important pillar of the national testing strategy to rapidly screen for infections on site during the SARS-CoV-2 pandemic. The current surge in infection rates around the globe is driven by the variant of concern (VoC) omicron (B.1.1.529). Here, we evaluated the performance of nine SARS-CoV-2 RATs in a single-centre laboratory study. We examined a total of 115 SARS-CoV-2 PCR-negative and 166 SARS-CoV-2 PCR-positive respiratory swab samples (101 omicron, 65 delta (B.1.617.2)) collected from October 2021 until January 2022 as well as cell culture-expanded clinical isolates of both VoCs. In an assessment of the analytical sensitivity in clinical specimen, the 50% limit of detection (LoD50) ranged from 1.77 × 106 to 7.03 × 107 RNA copies subjected to the RAT for omicron compared to 1.32 × 105 to 2.05 × 106 for delta. To score positive in these point-of-care tests, up to 10-fold (LoD50) or 101-fold (LoD95) higher virus loads were required for omicron- compared to delta-containing samples. The rates of true positive test results for omicron samples in the highest virus load category (Ct values < 25) ranged between 31.4 and 77.8%, while they dropped to 0-8.3% for samples with intermediate Ct values (25-30). Of note, testing of expanded virus stocks suggested a comparable RAT sensitivity of both VoCs, questioning the predictive value of this type of in vitro-studies for clinical performance. Given their importance for national test strategies in the current omicron wave, awareness must be increased for the reduced detection rate of omicron infections by RATs and a short list of suitable RATs that fulfill the minimal requirements of performance should be rapidly disclosed.
Insights
Rapid antigen tests (RATs) show reduced detection rates for the Omicron variant of SARS-CoV-2. Higher viral loads are needed for accurate Omicron detection, impacting public health strategies during the pandemic.
Area of Science:
- Virology and Infectious Diseases
- Diagnostic Test Performance Evaluation
- Public Health Surveillance
Background:
- Rapid antigen tests (RATs) are crucial for SARS-CoV-2 screening during the pandemic.
- The Omicron variant (B.1.1.529) is currently driving a global surge in infections.
- Evaluating RAT performance against emerging variants is essential for effective testing strategies.
Purpose of the Study:
- To assess the performance of nine SARS-CoV-2 rapid antigen tests (RATs).
- To compare the analytical sensitivity of RATs for detecting Omicron versus Delta variants.
- To inform national testing strategies during the Omicron wave.
Main Methods:
- Laboratory-based evaluation of nine SARS-CoV-2 RATs using clinical respiratory swab samples.
- Analysis of 115 PCR-negative and 166 PCR-positive samples (Omicron and Delta variants).
- Determination of the limit of detection (LoD50 and LoD95) for each RAT and variant.
Main Results:
- RATs required significantly higher viral loads (up to 10-101 fold) to detect Omicron compared to Delta.
- True positive rates for Omicron were substantially lower, especially in samples with intermediate viral loads (Ct 25-30).
- In vitro studies with expanded virus stocks showed comparable sensitivity for both variants, contrasting with clinical specimen results.
Conclusions:
- Current SARS-CoV-2 RATs exhibit reduced sensitivity for detecting the Omicron variant in clinical specimens.
- The clinical performance of RATs may not be accurately predicted by in vitro studies using expanded virus stocks.
- Increased awareness of RAT limitations with Omicron is critical; a list of suitable RATs should be rapidly disclosed.
