Some At-Home Tests May Miss Omicron in Early Stages of Infection

Thursday, January 6, 2022 — The Abbott BinaxNOW and Quidel QuickVue test — two widely used at-home rapid COVID tests — may sometimes fail to detect evidence of the Omicron variant in the first days after infection, even when people carry initial research indicates Having high levels of virus.

The researchers focused on 30 people with COVID in five workplaces that experienced what was likely an outbreak of the Omicron variant last month. Subjects received both saliva-based PCR tests (the gold standard) and rapid antigen-based tests that include nasal swabs.

Researchers report that it took, on average, three days for people to test positive on two rapid antigen tests after their first positive PCR result. In four cases, people transmitted the virus to others after a negative result, according to the study, which has not yet been peer-reviewed.

It is not yet clear whether the infection was missed because antigen tests are inherently less sensitive to omicron or because saliva tests may be better at detecting the new variant, New York times mentioned.

One possible explanation? Experts said Omicron may multiply faster or in the throat and mouth earlier than in the nose.

“While we have to wait to see if the science pays off, this could be an indication that this is where the virus first grows,” said Gigi Gronval, an immunologist and testing expert at the Johns Hopkins Bloomberg School of Public Health. times. “So if you were to look for the virus, which the tests do, you might find more of it faster in a throat swab over the nose.”

There have also been reports that some people whose initial test results were negative in antigen tests when they swabbed the inside of their nose got a positive result when they swept the back of their throat.

“There’s a lot of talk about this,” said Nathan Grubow, a virologist at the Yale School of Public Health. times. “This obviously warrants further investigation.”

The latest study is consistent with other preliminary evidence that the at-home tests that many Americans rely on may fail to detect some cases of Omicron in the early days of infection.

“The message is not that we should stop using these tests,” said Isabella Eckerl, a clinical virologist at the University of Geneva, Switzerland. times.

But people should remain vigilant after getting negative results, especially when they show symptoms or think they may have been exposed to the virus.

“It’s not a ticket that allows you to get back to normal or drop any other measures,” Eckerl said.

Why might you miss the Omicron Rapid Tests in the early stages of an infection? It is designed to detect proteins on the surface of the coronavirus. Experts said that if mutations in the virus alter the structure of these proteins, alternative antigen tests may be lost.

The researchers said they shared their findings with federal officials in real time, as the outbreak was occurring last month.

Study author Dr. Ruby Sika told The times.

The study comes a week after the US Food and Drug Administration released its own update on the effectiveness of rapid antigen tests. “Early data suggests that antigen tests detect an omicron variant but may have reduced sensitivity,” the agency said in a statement.

Many of these studies are early and small, and more data is needed. Scientists said that the tests can achieve results at home in minutes and that positive results are more reliable. This is an important tool along with PCR tests that can take days to come back.

The Omicron variant contains about 50 mutations, including more than 30 on the spike protein alone. Most rapid antigen tests are designed to detect more stable targets, and times mentioned.

In September, the Food and Drug Administration told rapid test makers that they would be asked to continue testing their products as new variants emerge, and if asked to share those results with the agency, the newspaper said.

Several companies have announced that their tests can detect Omicron, and several independent scientists have said they believe the tests should be able to identify the variant, especially when it is present at high levels. But the new studies raise questions about the sensitivity of the tests.

Bruce Trumpberg, director of the National Institute of Medical Imaging and Bioengineering, told times. The scientists evaluated antigen tests using pooled nasal swab samples collected from people with either the Omicron variant or the Delta variant.

Then they diluted each of these pooled samples until antigen tests stopped detecting the virus. They found that the tests may be less sensitive to the new variant, Tromberg said. However, he added, in real-world environments, “it may not translate to any different sensitivity.”

FDA spokeswoman Stephanie Kakumo told times Last week studies were underway to “confirm the cause of the apparent decreased sensitivity”.

“Once this is known, each developer can make adjustments to existing tests with FDA support, if appropriate,” she said.

The FDA update wasn’t the first sign of reduced sensitivity with rapid tests. Eckerle and her colleagues recently evaluated seven antigen tests against samples of virus cultured from samples taken from people infected with Omicron. In general, the researchers found that the tests were less sensitive to omicron than previous variants.

“They missed samples of an infectious virus, and they missed samples with a very good viral payload,” Eckerl said. The work was published in December on a prepress server.

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