Why Antigen Tests May Still Work Well for Omicron Despite “Reduced Sensitivity” in Laboratory Studies

The first research supported by the National Institutes of Health on several COVID-19[female[feminine antigen tests suggest that the kits will still work to detect cases of Omicron variant despite “reduced sensitivity” seen in early lab studies with some brands, federal health officials said Wednesday.

NIH-backed scientists rushed to conduct experiments to assess Omicron’s impact on antigen test performance, compared to previous strains of the virus. the rapid tests, which can be done at home, have gained popularity amid a record peak of COVID-19 cases this month.

The Food and Drug Administration said Tuesday that some antigen tests may have “reduced sensitivity” for Omicron, citing early data from NIH lab studies. Lower sensitivity means there might be a greater chance of missing traces of the virus and giving false negative results. However, NIH scientists warn that their lab findings are not evidence of a significant drop in the actual performance of popular home tests, even in the “worst-case scenario.”

“A change in sensitivity in the laboratory is no guarantee that there is a change in sensitivity from a clinical point of view. I would not recommend that people suddenly give up their antigen tests,” says Bruce Tromberg. , director of the National Institute of Biomedical Imaging. and bioengineering.

Tromberg heads the NIH RADx program which covers much of the Biden administration’s efforts to speed up COVID-19 testing. The initiative paved the way for the FDA to give the green light to new tests, including guiding the recent permissions over-the-counter tests from Siemens and Roche. A program-backed task force has also been evaluating variants of concern since last January, investigating how they might interfere with permitted tests in the United States.

Through the program, scientists at Emory University have collected samples from Omicron patients across the country. These samples are pooled in their laboratory, then gradually diluted until standard tests no longer detect the virus in the mixture.

Compared to similar experiments the lab has conducted previously, Tromberg said scientists initially found that antigen testing was still able to detect roughly Omicron cases as well as previous variants using samples. “Heat inactivated”. But later, when studying various brands of antigen tests using pools of “live viruses”, some were only able to detect the virus in more concentrated mixtures of Omicron compared to the Delta variant.

Enough data to better measure whether this change significantly affects the “clinical” performance of antigen tests – their actual effectiveness in detecting the virus in humans – could be gathered in a matter of weeks, Tromberg guessed. Beyond the efforts of the NIH and the FDA, researchers from test manufacturers, universities and health authorities abroad are also examining the ability of antigen tests to detect Omicron cases in the real world.

“It could be that the sensitivity in the clinic has gone down. It could be that the sensitivity is the same. It could even be better. We have certainly seen that too. So it is still very early to tell and we have to fill this out. photo, “said Tromberg.

Companies that provide several home testing options, including the Abbott Binax NOW, Quidel QuickVue, Illuminated, and Roche SD Biosensor tests, recently released statements indicating that the data suggests their tests will work the same for Omicron as with previous variants.

A spokesperson for Access Bio said they are still working to submit updated performance ratings for their CareStart test to NIH, but their products can detect Omicron with “the same sensitivity when tested with a recombinant protein “of the variant.

Experts say other factors could also impact the ability of antigen tests to detect Omicron beyond the lab, ranging from where the new variant first infects the body – for example, in the upper respiratory tract compared to the lungs – with signs that it may have a shorter incubation period and lead to higher virus loads. Repeating the test two days in a row also improves the chances that antigen tests can detect infections.

“When dealing with an antigen test, everyone knows from the start that it is not, by the nature of the technical aspect of the test, as sensitive as a PCR,” said Dr Anthony. Fauci, Chief Medical Advisor to the President, told reporters Wednesday.

Federal health officials have urged Americans to research COVID-19 tests ahead of holiday gatherings, even if they have received a recall, as a further way to curb the unprecedented spread of Omicron. The rate of new cases is records nationwide and could be enough to overwhelm hospitals in parts of the country, despite signs Omicron is a problem lower risk of serious illness.

“The fact that the sensitivity is somewhat diminished does not eliminate the importance of the benefit and usefulness of these tests in different circumstances,” said Fauci.

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