Comparison of Rapid Antigen Tests' Performance Between Delta and Omicron Variants of SARS-CoV-2 : A Secondary Analysis From a Serial Home Self-testing Study

Abstract

Background: It is important to document the performance of rapid antigen tests (Ag-RDTs) in detecting SARS-CoV-2 variants.

Objective: To compare the performance of Ag-RDTs in detecting the Delta (B.1.617.2) and Omicron (B.1.1.529) variants of SARS-CoV-2.

Design: Secondary analysis of a prospective cohort study that enrolled participants between 18 October 2021 and 24 January 2022. Participants did Ag-RDTs and collected samples for reverse transcriptase polymerase chain reaction (RT-PCR) testing every 48 hours for 15 days.

Setting: The parent study enrolled participants throughout the mainland United States through a digital platform. All participants self-collected anterior nasal swabs for rapid antigen testing and RT-PCR testing. All Ag-RDTs were completed at home, whereas nasal swabs for RT-PCR were shipped to a central laboratory.

Participants: Of 7349 participants enrolled in the parent study, 5779 asymptomatic persons who tested negative for SARS-CoV-2 on day 1 of the study were eligible for this substudy.

Measurements: Sensitivity of Ag-RDTs on the same day as the first positive (index) RT-PCR result and 48 hours after the first positive RT-PCR result.

Results: 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%] vs. Omicron, 22.1% [CI, 15.5% to 28.8%]; at 48 hours: Delta, 44.8% [CI, 32.0% to 57.6%] vs. 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%] vs. 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 1 week; those with Delta infections remained consistently negative on Ag-RDTs.

Limitation: A testing frequency of 48 hours does not allow a finer temporal resolution of the analysis of test performance, and the results of Ag-RDTs are based on self-report.

Conclusion: The performance of Ag-RDTs in persons infected with the SARS-CoV-2 Omicron variant is not inferior to that in persons with Delta infections. Serial testing improved the sensitivity of Ag-RDTs for both variants. The performance of rapid antigen testing varies on the basis of duration of RT-PCR positivity.

Primary funding source: National Heart, Lung, and Blood Institute of the National Institutes of Health.

Visual Abstract.. Rapid Antigen Test Performance for Delta vs. Omicron SARS-CoV-2 Variants.

Use of rapid tests for diagnosis of COVID-19 is now commonplace, but questions remain regarding their performance characteristics compared with those of polymerase chain reaction testing. The role of sequential rapid testing in improving sensitivity is of great interest.

Figure 1.. Study flow diagram.

5779 participants were included in this study, representing 45 958 participant-days of testing. 207 participants had a new-onset positive result on RT-PCR testing (58 Delta and 149 Omicron) (population A). The subanalysis was based on the result of RT-PCR testing 48 h after the initial positive RT-PCR result (populations B, C, and D). Ag-RDT = rapid antigen test; RT-PCR = reverse transcriptase polymerase chain reaction.

Figure 2.. Proportion of participants testing positive by Ag-RDT, by days since initial sample collection for positive RT-PCR result.

Proportion of RT-PCR–positive participants who tested positive by Ag-RDT did not significantly differ between Delta and Omicron infections. Ag-RDT performance improved when tests were used serially. Ag-RDT = rapid antigen test; RT-PCR = reverse transcriptase polymerase chain reaction.