Rapid Antigen Tests Detect Omicron, Delta SARS-CoV-2 Variants

Accurate and accessible testing for SARS-CoV-2 is a critical tool for the timely identification of infection to inform isolation recommendations, prevent transmission, and facilitate early initiation of therapy to reduce disease progression.

Rapid antigen tests for COVID-19 show great promise as a testing method that is easy to use, accessible, and cost-effective Rapid antigen tests (Ag-RDTs) have lower sensitivity than RT-PCR tests for detecting SARS-CoV-2, however, sensitivity can be improved through serial testing.

A large team of medical scientists at the University of Massachusetts Chan Medical School, Worcester, MA, USA) compared the performance of Ag-RDTs in detecting the Delta (B.1.617.2) and Omicron (B.1.1.529) variants of SARS-CoV-2. The team relied on data from the prospective cohort study Test Us At Home in which participants serially took both at-home antigen and send-in PCR COVID-19 tests over a period of 10 to 15 days. This analysis focuses on the 5,779 individuals who tested negative for SARS-CoV-2 at the start of the parent study and the 207 individuals of those who later tested positive for the virus by PCR.

On enrollment, participants were assigned to 1 of 3 Ag-RDTs with emergency use authorization: BD Veritor At-Home COVID-19 Test (Becton, Dickinson and Company, San Diego, CA, USA), Quidel QuickVue At-Home OTC COVID-19 Test (San Diego, CA, USA) and Abbott BinaxNOW COVID-19 Antigen Self-Test (Princeton, NJ, USA). Participants received the Ag-RDT and the Quest Diagnostics collection kit for COVID-19 by mail at the shipping address provided on enrollment.

The investigators reported that a total of 207 participants were positive on RT-PCR (58 Delta, 149 Omicron). Differences in sensitivity between variants were not statistically significant (same day: Delta, 15.5% [95% CI, 6.2% to 24.8%] versus Omicron, 22.1% [CI, 15.5% to 28.8%]; at 48 hours: Delta, 44.8% [CI, 32.0% to 57.6%] versus Omicron, 49.7% [CI, 41.6% to 57.6%]). Among 109 participants who had RT-PCR–positive results for 48 hours, rapid antigen sensitivity did not differ significantly between Delta- and Omicron-infected participants (48-hour sensitivity: Delta, 81.5% [CI, 66.8% to 96.1%] versus Omicron, 78.0% [CI, 69.1% to 87.0%]). Only 7.2% of the 69 participants with RT-PCR–positive results for shorter than 48 hours tested positive by Ag-RDT within one week; those with Delta infections remained consistently negative on Ag-RDTs.

The authors concluded that nasal swab Ag-RDT performance was similar between the Omicron and Delta variants. In both cases, detection of virus with Ag-RDTs was associated with relative viral load as measured by Ct value. The data suggest that serial testing continues to be important in improving the performance of Ag-RDTs. Future work to increase the understanding of persons with singleton RT-PCR positivity is needed to determine the public health significance of a false-negative Ag-RDT result in this subpopulation. The study was published on October 11, 2022 in the journal Annals of Internal Medicine.

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