Analytical and clinical evaluation of antigen-based rapid diagnostic tests against essentially the most encountered SARS-CoV-2 variants

A recent study posted on the medRxiv* preprint server has assessed the sensitivity of antigen-based rapid diagnostic tests (Ag-RDTs). 

*Necessary notice: medRxiv publishes preliminary scientific reports that aren’t peer-reviewed and, subsequently, shouldn’t be considered conclusive, guide clinical practice/health-related behavior, or treated as established information.

Background

The rapid spread of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) led to the coronavirus disease 2019 (COVID-19) pandemic.

To be able to combat this pandemic, it is incredibly essential to forestall further transmission of infection. To realize this, it’s imperative to discover SARS-CoV-2-infected individuals and isolate them from healthy individuals quickly.

Ag-RDTs could be performed at home by lay individuals to detect an infection. These diagnostic tests are inexpensive, don’t require expert personnel, and supply results rapidly.

Within the context of the COVID-19 pandemic, Ag-RDTs have played a vital role in controlling disease transmission. Nonetheless, the efficiency of those tests has been challenged by the emergence of latest SARS-CoV-2 variants.

The undetected SARS-CoV-2 variants of concern (VOC) have particularly threatened to trigger latest waves of world infections.

At present, the SARS-CoV-2 Omicron (B.1.1.529) variant, which has been classified as a VOC, is dominantly circulating in most countries the world over. A complete of 5 Omicron sub-lineages, namely, BA.1, BA.2, BA.3, BA.4, and BA.5, have been identified as of March 2023.

The Omicron variant accommodates the best variety of mutations throughout the genome that include spike (S), envelope (E), membrane (M), and nucleocapsid (N) protein regions. 

Most Ag-RDTs have been developed targeting the N protein of the wild-type (WT) SARS-CoV-2 (ancestral strain). Preliminary analytical and clinical assessments of a small variety of brands have presented contradictory data about the efficacy of existing Ag-RDTs against the Omicron variant. 

Concerning the study

On this study, a complete of 34 commercially available COVID-19 Ag-RDTs were assessed for the detection of the Omicron VOC (BA.1 and BA.5). Moreover, this finding was compared with the sensitivity against Alpha, Gamma, and Delta VOCs and WT. 

All Ag-RDTs evaluated on this study were based on lateral flow assays (LFA). Here, thirty-one of the Ag-RDTs used colorimetric gold nanoparticle detection, two used fluorescence, and one used microfluidic immunofluorescence technology.

All clinical samples were obtained from the ‘Facilitating Accelerated Clinical Evaluation of Novel Diagnostic Tests for COVID-19’ (FALCON) study. Nasopharyngeal (NP) swabs were collected from symptomatic participants who visited the COVID-19 test center in Liverpool John Lennon Airport, UK, between January 2021 and March 2022. 

Study findings

Out of the 34 tests that were analyzed, 31 Ag-RDTs exhibited sensitivity for Omicron sub lineage BA.5. This evaluation was based on plaque forming units per milliliter (pfu/mL), fulfilling the factors set by the British Department of Health and Social Care (DHSC).

As per the recommendations of the World Health Organization (WHO), the limit of detection (LOD) of Omicron VOC BA.5 was significantly lower than the WT and the Alpha VOC. Nonetheless, the LOD value was just like the Gamma, Delta, and Omicron BA.1 VOCs.

Only 23 Ag-RDTs exhibited sensitivity for Omicron BA.1. Taken together, these tests exhibited a significantly lower LOD with Omicron BA.5 in comparison with all other VOCs and WT. This high sensitivity against BA.5 could possibly be attributed to the indisputable fact that BA.5 doesn’t have any lineage-defining mutations within the N gene.

Clinical evaluations were performed on five out of thirty-four Ag-RDT brands. In comparison with all tested Ag-RDTs brands, Onsite exhibited one of the best overall sensitivity, while Hotgen consistently performed poorly.

Strengths and limitations

The present study has several strengths, including the great evaluation of the analytical sensitivity of 34 commercially available Ag-RDT brands. Moreover, all assessments were based on each viral isolates and clinical specimens.

Considered one of the important thing limitations of this study is using retrospective frozen specimens as a substitute of fresh swabs, as suggested by nearly all of Ag-RDT manufacturers.

Nonetheless, to rectify the potential of potential RNA degradation after a freeze-thaw cycle, SARS-CoV-2 RNA was re-evaluated by RT-PCR on the time of conducting the Ag-RDT test.

One other limitation of this study is that the LOD experiments for the WT, Alpha, and Gamma viral isolates weren’t repeated. The present study used data from previously conducted experiments using an identical protocol, and these findings were compared with the brand new data for the Omicron and Delta variants.

Conclusions

The present study highlighted similar, if not higher, LODs for the Omicron variant in comparison with other non-Omicron VOCs. Notably, each analytical and clinical assessments revealed a decreased sensitivity of the tested Ag-RDTs for Delta VOC.

In the long run, commercially available Ag-RDTs have to be continually assessed, especially those really helpful for home testing, for his or her sensitivity for all SARS-CoV-2 VOCs, including the Delta variant. 

*Necessary notice: medRxiv publishes preliminary scientific reports that aren’t peer-reviewed and, subsequently, shouldn’t be considered conclusive, guide clinical practice/health-related behavior, or treated as established information.