While the rapid antigen COVID tests remain a useful tool for the detection of COVID-19 infections, continuous assessment and updating is likely needed in the context of variants of concern, according to research published in the Journal of Clinical Microbiology.

In a recent study, scientists at the Harvard T.H. Chan School of Public Health and Beth Israel Deaconess Medical Center used live virus culture to assess how well four rapid antigen COVID tests are able to detect these variants of concern.

Using three strains of cultured live virus, the team assessed differences in the limits of detection (LoD) – the smallest amount of viral antigen detectable at 95% certainty – of four commercially available rapid antigen COVID tests: the Binax, CareStart, GenBody and LumiraDx tests.

The researchers found that all four tests were as sensitive to the Omicron variant, if not more, as they were to original SARS-CoV-2 viral strain, known as WA1. Three rapid antigen COVID tests, however, showed less sensitivity to the Delta strain, with only the CareStart demonstrating equal detection of all three strains.

“Unlike the sensitive molecular tests that detect multiple SARS-CoV-2 genes, rapid antigen COVID tests target a single viral protein,” said co-corresponding author James Kirby, MD, director of the Clinical Microbiology Laboratory at BIDMC. “As the pandemic continues, however, some hypothesize that the performance of available antigen test may vary among the COVID variants of concern.”

“We expect that the observed loss in Delta sensitivity could have resulted in a 20% or more loss of detection in potentially infectious individuals – nevertheless, the most infectious individuals still should have been detected,” said Kirby, also a professor of pathology at Harvard Medical School. “However, our findings suggest that antigen test performance needs to be reevaluated for emerging variants to ensure they still meet the intended public health testing goals of the pandemic.”