Performance of Rapid Antigen Tests in Identifying Omicron Ba.4 and Ba.5 Infections in South Africa

Abstract

Background: Concerns around accuracy and performance of rapid antigen tests continue to be raised with the emergence of new SARS-CoV-2 variants.ObjectiveTo evaluate the performance of two widely used SARS-CoV-2 rapid antigen tests during BA.4/BA.5 SARS-CoV-2 wave in South Africa.

Study design: A prospective field evaluation compared the SARS-CoV-2 Antigen Rapid test from Hangzhou AllTest Biotech (nasal swab) and the Standard Q COVID-19 Rapid Antigen test from SD Biosensor (nasopharyngeal swab) to the Abbott RealTime SARS-CoV-2 assay (nasopharyngeal swab) on samples collected from 540 study participants.

Results: Overall 28.5% (154/540) were SARS-CoV-2 RT-PCR positive with median Ct value of 12.3 (IQR 9.3-19.4). The sensitivity of the AllTest SARS-CoV-2 Ag test and Standard Q COVID-19 Ag test was 73.38% (95% CI 65.89-79.73) and 74.03% (95% CI 66.58-80.31) and their specificity was 97.41% (95% CI 95.30-98.59) and 99.22% (95% CI 97.74-99.74) respectively. Sensitivity was >90% when the Ct value was <20. The sensitivity of both rapid tests was >90% in samples infected with Omicron sub-lineage BA.4 and BA.5..

Conclusion: The accuracy of both rapid antigen tests that target the nucleocapsid SARS-CoV-2 protein, were not adversely affected by the emergence of BA.4 and BA.5 Omicron sub-variants.

Note:
Funding Information: This project was funded as part of FIND's work as co-convener of the diagnostics pillar of the Access to COVID-19 Tools (ACT) Accelerator, including support from The Swiss Agency for Development and Cooperation [grant number 81066910]. Research presented here was partly funded by the European & Developing Countries Clinical Trials partnership (EDCTP): RIA2020EF-2928 - Mobilisation of research funds for COVID-19 as a Public Health Emergency and the South African Department of Science and Innovation (DSI) Top-up funding to strengthen EDCTP COVID-19 regional networks.

Declaration of Interests: Antigen rapid diagnostic tests were provided by FIND, the global alliance for diagnostics, and FIND was involved in the study design development. CE and MdV are employees of FIND. The rest of the authors declare no conflict of interests.

Ethics Approval Statement: The study was approved by the KwaZulu-Natal Biomedical Research Ethics Committee (BREC approval No: BREC/00001195/2020 and BREC/00003106/2021).

Keywords: SARS-CoV-2, COVID-19, antigen, omicron, BA.4, BA.5