A small, but real-world study shows that two popular home antigen tests, Quidel QuickVue and Abbott BinaxNOW, may fail to detect Omicron infections even in cases of high coronavirus levels.
The study, which is not yet peer-reviewed by the scientific community, focused on 30 people infected by the virus at five workplaces that experienced Omicron variant outbreaks in December. Both saliva-based P.C.R. and nasal swabs were administered to the participants. tests and rapid antigen testing using nasal swabs.
On average, it took three days for people who had previously tested positive for P.C.R. to test positive on a rapid-antigen test. result. According to the study, four people passed the virus to others, while rapid testing showed a negative result. The study was done by several members from the Covid-19 Sports and Society Working Group.
It is unclear if the infections were missed by Omicron antigen tests that are less sensitive or saliva tests that detect the new variant.
But the results are consistent with other preliminary evidence that the at-home tests that many Americans have come to rely on — at least as currently administered, with a nasal swab — may fail to detect some Omicron cases in the first days of infection.
The researchers said they shared their results with federal officials — including at the White House, the Food and Drug Administration and the Centers for Disease Control and Prevention — in real-time, as the outbreaks were occurring last month.
“They’re aware that there are flaws with antigen testing,” said Dr. Robby Sikka, an author of the study and chair of the working group.
The study comes just a week after the Food and Drug Administration issued its own update on the effectiveness and efficiency of the rapid antigen test. “Early data suggests that antigen tests do detect the Omicron variant but may have reduced sensitivity,” the agency said.
Many of these studies are small and early in their development, so more data is needed. Many scientists agree that these tests are an important tool for public health. They can be done at home in a matter of minutes. Positive results are more likely to be informative. (The P.C.R. wait can be days. The wait for P.C.R. results can be days.
“The message is not that we should stop using these tests,” said Isabella Eckerle, a clinical virologist at the University of Geneva in Switzerland.
People should not interpret negative results as a sign of infection, especially if they have symptoms and believe they may have been exposed.
“It’s not a ticket that allows you to go back to normal or to drop any other measures,” Dr. Eckerle said.
Antigen tests can detect proteins on the coronavirus’s surfaces. Antigen tests might not detect a variant if there are mutations in the virus’s structure.
There are about 50 mutations in Omicron’s variant, with 30 of them on the spike protein. Rapid antigen tests are used to detect stable targets that are less mutated in Omicron.
Still, even minor-seeming mutations can affect a virus’s surface proteins, “sometimes in non-obvious ways,” said John Moore, a virologist at Weill Cornell Medicine. “Only experimental data can determine whether there is an impact or not.”
F.D.A. In September, the F.D.A. told rapid testers that they would have to continue testing their products for new variants and, if required, share those results with agency personnel.
Many companies have claimed that their Omicron-detecting tests can detect the variant. Independent scientists also stated that they believe that the tests should recognize it, especially when it’s present at high levels. But a few new studies raise questions about the tests’ sensitivity.
The F.D.A.’s update stemmed from an evaluation it is doing with the National Institutes of Health, said Bruce Tromberg, director of the National Institute of Biomedical Imaging and Bioengineering. The scientists tested for antigens using nasal mucus from multiple Omicron patients, as well as similar samples from Delta patients.
Scientists then diluted the pooled samples until they could no longer detect the virus. Dr. Tromberg explained that the tests were able detect more delta samples than Omicron ones, suggesting that they may be less sensitive. Still, he added, in real-world settings, “it may not translate into any different sensitivity.”
F.D.A. spokeswoman, Stephanie Caccomo, said last week that studies were underway “to confirm the reason for the apparent decreased sensitivity.”
“Once that is known,” she said, “adjustments to existing tests can be undertaken by each developer with support from the F.D.A., if appropriate.”
F.D.A. The F.D.A. update was not the first indication that some antigen tests might be less sensitive to Omicron. Dr. Eckerle and her collaborators recently evaluated seven antigen tests against Omicron virus samples taken from Omicron-infected people. The tests were less sensitive than previous Omicron variants, according to the researchers.
“They missed samples with infectious virus, and they missed samples that had quite a decent viral load,” Dr. Eckerle said. The work has not yet appeared in a scientific journal.
There was also a lot of variability in the results of the various tests, many of which are not available in America. A study in Australia found that most of the antigen tests had the same sensitivity as Omicron and Delta.
Experts say more data is required.
“Each test is going to have to be evaluated independently any time there’s 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 only on five New York and California offices that experienced virus outbreaks in December. P.C.R. revealed a clear genetic pattern in 29 of 30 patients. These tests suggested that Omicron was most likely to have infected these people.
Each participant received P.C.R. Over a period of 10 days, each participant was tested for antigens daily. The most discordant results were found in the first three days after infection.
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“A negative result may not actually be a negative result,” said Anne Wyllie, a microbiologist at the Yale School of Public Health and an author of the new study. “People should not ignore high risk exposures. They should not ignore symptoms.”
The study’s other authors are Blythe Adamson, the founder of Infectious Economics, a public health consulting company, and Dr. Prem Premsrirut, the chief executive of Mirimus Laboratories, which offers saliva-based P.C.R. testing.
John Koval, an Abbott spokesperson, stated Wednesday that the finding that a P.C.R. was more sensitive than expected was “not new”. test is more sensitive is “not new.”
“Due to immediate turnaround time, frequent rapid antigen testing does slow transmission — and with a highly infectious variant frequent testing is needed, which is not realistic with P.C.R.,” he wrote in an email.
Quidel’s president, Douglas Bryant, said in a statement that the company performed recent testing using samples from South Africa and confirmed that its rapid tests are detecting the Omicron variant.
A spokesperson for the company said that saliva-based P.C.R. was not surprising. Tests detected the virus faster than nasal swabs, if the study was correct. The company pointed out that the rapid tests it uses only have F.D.A. authorization to collect nasal swab samples.
Five participants who used both saliva-based P.C.R. and nasal methods were included in a smaller study. The researchers discovered that virus levels in saliva samples rose to the surface a day or so before they reached the nose.
These findings are consistent with a South African report that has not been reviewed by experts. The researchers discovered that P.C.R. tests picked up a higher share of Omicron infections when saliva samples — produced by the rubbing of a swab inside the cheeks, around the gums and tongue — were used instead of nasal samples. For Delta, the reverse was true.
“Ideally, until we can directly compare the relative sensitivity of the antigen tests, my suggestion would be to test both sites,” Diana Hardie, a clinical virologist at the University of Cape Town, who led the research, said in an email.
Omicron may be reproducing faster in the throat and mouth than it does in the nose, which could explain the findings.
“While we’ll have to wait to see if the science bears out, that might be an indicator that that’s where the virus is growing first,” said Gigi Gronvall, an immunologist at Johns Hopkins Bloomberg School of Public Health and a testing expert. “So if you’re going to look for the virus, which is what the tests do, then you may find more of it faster in the throat swab over the nose.”
Anecdotal reports also indicate that some people who test negative on antigen tests by swabbing inside their noses have positive results when they instead swab the back of it.
“There’s a lot of chatter around this,” said Nathan Grubaugh, a virologist at the Yale School of Public Health. “Obviously, that warrants further investigation.”
Some tests are only available in Britain and require that you swab the nose and throat. The antigen tests available here in the USA do not permit the collection of saliva, or samples from the throat.
Omicron’s rapid replication also means that there is a narrower window to catch the virus before it begins spreading, and that people may need to test themselves sooner after a potential exposure and as close as possible to an upcoming gathering or event, experts said. They may need to test themselves more often overall, which can be a challenge when tests are scarce.
Experts advise that anyone who has been exposed to the virus must undergo at least two antigen testing over the course of approximately two days.
Source: NY Times