Some At-Home Tests May Miss Omicron in Early Stages of Infection
The Abbott BinaxNOW and Quidel QuickVue rapid at-home COVID tests may sometimes fail to spot evidence of the Omicron variant in the first days after infection.
The researchers focused on 30 people infected with COVID at five workplaces that experienced what were most likely outbreaks of the Omicron variant last month. The people received both saliva-based PCR tests and rapid antigen-based tests involving nasal swabs.
It took three days, on average, for people to test positive on the two rapid antigen tests after their first positive PCR result, researchers reported. In four cases, people transmitted the virus to others after a negative result.
Reports have also surfaced that some people who initially tested negative on antigen tests when they swabbed inside their noses went on to receive a positive result when they swabbed the back of their throats.
The latest study is consistent with other preliminary evidence that the at-home tests that many Americans have come to rely on may fail to detect some Omicron cases in the early days of infection, but people should remain cautious after getting negative results, especially when they have symptoms or believe they may have been exposed to the virus.
Why might the rapid tests be missing Omicron in the early stages of infection? They are designed to detect proteins lying on the surface of the coronavirus. If mutations in the virus change the structure of these proteins, antigen tests might miss the variant, experts said.
The study comes a week after the U.S. Food and Drug Administration released its own update on the effectiveness of the rapid antigen tests. Early data suggests that antigen tests do detect the Omicron variant but may have reduced sensitivity.
Many of those studies are early and small, and much more data is needed. The tests can deliver results at home in minutes and positive results are more reliable, scientists have said. That's an important tool alongside PCR tests that can take days to come back.
In September, the FDA told makers of rapid tests that they would be required to continue to test their products as new variants emerged, and, if asked, to share those results with the agency.
Many companies have announced that their tests can detect Omicron, and several independent scientists said that they believed the tests should be capable of recognizing the variant, especially when present at high levels, but the new studies raise questions about the tests’ sensitivity.
The FDA update was not the first sign of decreased sensitivity with the rapid tests. Overall, the researchers found, the tests were less sensitive to Omicron than to previous variants.
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