Emerging Data Raise Questions About Antigen Tests and Nasal Swabs

Small, new real world work He suggests that two commonly used home antigen tests, Abbott BinaxNOW and Quidel QuickVue, may not detect some Omicron infections even when people have high levels of coronavirus.

The study, which has not yet been peer-reviewed, focused on 30 people infected with the virus in five workplaces who experienced the most likely outbreaks of the Omicron variant in December. Humans underwent rapid antigen tests using both saliva-based PCR tests and nasal swabs.

On average, it took three days for people to test positive in the rapid antigen test after the initial positive PCR result. According to research led by several members of the Covid-19 Sports and Society Working Group, in four cases the rapid test showed a negative result when people were transmitting the virus to others.

It is unclear whether infections have been missed because antigen tests are inherently less sensitive to Omicron or because salivary tests may be better at detecting the new variant.

But the results are consistent with other preliminary evidence that the home tests that many Americans rely on—at least as currently administered with a nasal swab—may fail to detect some cases of Omicron in the early days of infection.

Because the outbreaks occurred last month, the researchers said they’ve shared their results in real-time with federal officials, including the White House, the Food and Drug Administration, and the Centers for Disease Control and Prevention.

The author of the study and the head of the study group, Dr. “They’re aware that there are flaws with antigen testing,” said Robby Sikka.

Study comes one week after Food and Drug Administration released its own update on the effectiveness of rapid antigen tests. “Early data suggest that antigen tests detect the Omicron variant but have decreased sensitivity,” the agency said.

Most studies are early and small, and much more data is needed. Many scientists said testing at home with results within minutes remains an important public health tool, and positive results are likely to be particularly informative. (PCR results can take days to wait.)

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

But people should be careful about interpreting negative results, especially when they have symptoms or believe they may have been exposed to the virus.

Dr. “This is not a ticket that lets you go back to normal or drop other measures,” Eckerle said.

Antigen tests are designed to detect proteins on the surface of the coronavirus. If mutations in the virus change the structure of these proteins, antigen tests may fail to detect the variant.

This Omicron variant has about 50 mutationsIncluding more than 30 on spike protein alone. Most rapid antigen tests are designed to detect more stable targets that are much less mutated in Omicron.

Still, Even seemingly minor mutations can affect a virus’s surface proteins in “sometimes unclear ways”, said John Moore, a virologist at Weill Cornell Medicine. “Only experimental data can determine whether there is an effect.”

FDA in September told the makers of the rapid tests As new variants emerge, they will be asked to continue testing their products and, if desired, share these results with the agency.

Many companies have announced that their tests can detect Omicron, and several independent scientists said they believe the tests should be capable of recognizing the variant, especially when present at high levels. But a few recent studies raise questions about the sensitivity of the tests.

Bruce Tromberg, director of the National Institute of Biomedical Imaging and Bioengineering, said the FDA’s update was due to an evaluation with the National Institutes of Health. The scientists evaluated the antigen tests using similar pooled samples from Delta patients, as well as pooled samples of nasal mucus collected from multiple people with Omicron.

The scientists then diluted each of these pooled samples until antigen tests no longer detected the virus. Dr. Tromberg said the tests were able to detect more dilute Delta samples than Omicron samples, suggesting that the tests may be less sensitive to the new variant. Still, he added, “it may not translate into a different sensibility” in real-world settings.

FDA spokeswoman Stephanie Cacomo said last week that studies are ongoing “to confirm the cause of the apparent decreased sensitivity.”

“Once this is known,” he said, “adjustments to existing testing can be made by each developer, with the support of the FDA, if needed.”

The FDA update wasn’t the first hint that some antigen tests might be less sensitive to Omicron. Dr. Eckerle and colleagues recently evaluated the performance of seven antigen tests Against virus samples from samples from people infected with Omicron. Overall, the researchers found that the tests were less sensitive to Omicron than previous variants.

Dr. “They missed samples with infectious virus and samples with pretty good viral loads,” Eckerle said. The study has not yet been published in a scientific journal.

However, there were also large differences in the performance of the different tests, many of which were not available in the United States. And an Australian study that examined a mostly diverse collection of antigen tests It had a similar sensitivity to Omicron and Delta.

Experts said more data is needed.

“Each test will have to be evaluated independently when there is a new variant,” said David O’Connor, a virologist at the University of Wisconsin, Madison, who urged people not to stop using rapid tests. “And that takes some time.”

The new study focused on five New York and California workplaces that had virus outbreaks in December. In 29 out of 30, the virus samples produced an illustrative genetic pattern in PCR tests, suggesting that these individuals were most likely infected with Omicron.

Each participant received PCR and antigen tests daily for up to 10 days. Discordant results came overwhelmingly within the first three days of infection.

“A negative result may not actually be a negative result,” said Anne Wyllie, a microbiologist at the Yale School of Public Health and author of the new study. “People should not ignore their high-risk exposure. They should not ignore the symptoms.”

Other authors of the study are Blythe Adamson, founder of Infectious Economics, a public health consulting firm, and Dr. Prem Premsrirut.

Abbott spokesman John Koval said Wednesday that the finding that a PCR test is more sensitive is “not new”.

“Due to the sudden turnaround time, frequent rapid antigen testing slows transmission – and with a highly contagious variant, frequent testing is required, which is unrealistic with PCR,” he wrote in an email.

Douglas Bryant, president of Quidel, said: in a statement He said the company was conducting final tests using samples from South Africa and confirmed that its rapid tests had detected the Omicron variant.

A company spokesperson also said that if the study concludes that viral load peaks in saliva first, it’s not surprising that saliva-based PCR tests detect the virus before nasal swabs. The company noted that its rapid tests only have FDA clearance to collect nasal swab samples.

In a smaller analysis of five participants who received both nasal and saliva-based PCR tests, the researchers found that virus levels peaked in saliva samples a day or two before peaking in nasal samples.

These findings are a Latest report from South Africahas not yet been studied by experts. The researchers found that when using saliva samples produced by rubbing a swab on the inside of the cheeks, around the gums and tongue, instead of nose samples, PCR tests had a higher share of Omicron infections. The reverse was true for Delta.

“Ideally, my suggestion would be to test both sites until we can directly compare the relative sensitivity of antigen tests,” clinical virologist Diana Hardie of the University of Cape Town, who led the study, said in an email.

One possible explanation for the findings is that Omicron reproduces in the throat and mouth faster or earlier than in the nose.

“We’ll have to wait to see if the science holds up, but that may be an indication that the virus grew there in the first place,” he said. Gigi Gronvall, an immunologist and tester at the Johns Hopkins Bloomberg School of Public Health. “So if you’re going to look for the virus like the tests do, you can find more quickly on the throat swab over the nose.”

Anecdotal reports also revealed that some people who tested negative on antigen tests by crawling inside their noses got a positive result when they cleared the back of their throat instead.

“There’s a lot of chatter about it,” said Nathan Grubaugh, a virologist at the Yale School of Public Health. “Obviously, this warrants further investigation.”

Some tests available in the UK clearing both the nose and throat, however, antigen tests available in the United States are not authorized to collect saliva or samples from the throat.

Omicron’s rapid replication also means there is a narrower window to catch the virus before it begins to spread, and people may need to test themselves after a potential exposure and as soon as possible to an upcoming meeting or event, experts say. They may also need to test themselves more often in general, which is a particular challenge when tests fall short.

Experts said that people who may have been exposed to the virus should have at least two antigen tests for about two days.

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