OraSure InteliSwab™ Rapid Antigen Test Performance with the SARS-CoV-2 Variants of Concern-Alpha, Beta, Gamma, Delta, and Omicron

Abstract

The emergence of SARS-CoV-2 in the human population and the resulting COVID-19 pandemic have led to the development of various diagnostic tests. The OraSure InteliSwab^™ COVID-19 Rapid Test is a recently developed and FDA emergency use-authorized rapid antigen-detecting test that functions as a lateral flow device targeting the nucleocapsid protein. Due to SARS-CoV-2 evolution, there is a need to evaluate the sensitivity of rapid antigen-detecting tests for new variants, especially variants of concern such as Omicron. In this study, the sensitivity of the OraSure InteliSwab^™ Test was investigated using cultured strains of the known variants of concern (VOCs, Alpha, Beta, Gamma, Delta, and Omicron) and the ancestral lineage (lineage A). Based on dilution series in cell culture medium, an approximate limit of detection for each variant was determined. The OraSure InteliSwab^™ Test showed an overall comparable performance using recombinant nucleocapsid protein and different cultured variants, with recorded limits of detection ranging between 3.77 × 10⁵ and 9.13 × 10⁵ RNA copies/mL. Finally, the sensitivity was evaluated using oropharyngeal swabs from Syrian golden hamsters inoculated with the six VOCs. Ultimately, the OraSure InteliSwab^™ COVID-19 Rapid Test showed no decrease in sensitivity between the ancestral SARS-CoV-2 strain and any VOCs including Omicron.

Keywords: COVID-19; Delta; Omicron; SARS-CoV-2; rapid antigen-detecting test; variants of concern.

Figure 1

InteliSwab^™ Test detection ability for SARS-CoV-2 variants. Cell culture stocks of the variants were serially diluted, and viral load was measured by gRNA qRT-PCR. (a) Comparison of a positive InteliSwab^™ Test (left) and a negative InteliSwab^™ Test (right). (b) Box plots displaying the distribution of positive InteliSwab^™ Tests across the 6 variants compared to the Ct values, RNA copies/mL, and TCID₅₀/mL. The positive InteliSwabs^™ are from the 2-fold dilution series for each variant (from left to right, N = 145, 31, 27, 19, 30, 18, and 20). Shown is the median, minimum, and maximum. (c) Bar charts representing the percentage of positive InteliSwab^™ Tests compared to Ct values. Initial Ct values were rounded to the nearest whole number.

Figure 2

InteliSwab^™ results for SARS-CoV-2 variants in Syrian golden hamsters. For each variant, animals (N = 6) were inoculated with 1 × 10³ TCID₅₀/mL. Oropharyngeal swabs were taken for 7 days. (a) Box plots depicting viral load (gRNA) in swabs across the 7 days; box and whiskers represent the median, minimum, maximum, and individual Ct values. Gray lines represent the mean Ct value of oropharyngeal swabs for each day. Pie charts show results of oropharyngeal swabs tested by InteliSwab^™; blue = positive; orange = negative. For b and c, statistical significance was measured by the Kruskal–Wallis test. (b) Box plots showing cumulative (area under the curve (AUC) analysis) respiratory shedding of SARS-CoV-2 variants viral load in oropharyngeal swabs measured by gRNA. Box and whiskers represent the median, minimum, and maximum cumulative respiratory shedding. For lineage A and Omicron, p = 0.0083. For Alpha and Omicron, p = 0.0385. (c) Box plots representing the positive OraSure InteliSwabs^™ from all oropharyngeal swabs measured across the 7 days. Box and whiskers represent the median, minimum, and maximum Ct values (from left to right, N = 35, 28, 38, 32, 26, and 10), ns = not significant.