Now the FDA says rapid tests for Covid antigens may be less sensitive in detecting Omicron variant - causing 'false negative' results
Rapid antigen tests for Covid may be less sensitive in detecting the Omicron variant and are leading to 'false negatives,' the Food and Drug Administration said Tuesday.
The FDA made preliminary findings using samples from patients confirmed to be infected with the new mutant strain.
The federal agency said early results show that antigen tests 'do detect the Omicron variant but may have reduced sensitivity,' meaning it's possible the tests could miss an infection, known as a 'false negative.'
It's not clear which brand of lateral flow tests the FDA were using in their study or to what degree there was reduced sensitivity.
According to a meta-analysis of studies by the Cochrane Library, lateral flow tests detect an average of 72 percent of symptomatic cases and 58 percent of asymptomatic ones.
This could be the reason for their reduced sensitivity with Omicron because the new strain generally presents with milder symptoms and it is more likely than with previous variants to produce no symptoms at all.
The report comes as cases skyrocketed to record levels on Tuesday - with a seven-day average 254,496 infections - prompting high demand for at-home rapid tests which are in short supply.
Joe Biden has promised 500 million rapid tests for US households for free starting in January and the FDA also plans to set up new testing sites in addition to 20,000 already in operation.
The move comes after Amazon, CVS and Walgreens last week limited how many tests each customer could buy to cope with the surging demand.
The rapid tests can be done at home, with results in minutes, while PCR tests are processed in labs and have turnaround times that can take several days.
The FDA didn't say that people should not use the antigen tests.
'The FDA continues to authorize the use of these tests as directed in the authorized labeling and individuals should continue to use them in accordance with the instructions included with the tests,' the agency said.
'Antigen tests are generally less sensitive and less likely to pick up very early infections compared to molecular (PCR) tests.'
Gigi Gronvall, a senior researcher at the Johns Hopkins Center for Health Security, told NBC that the evolution of the virus meant it was harder to accurately detect.
'With with every new variant, we have to make sure that the tests work, and it looks like the tests work for this. But they're not picking up infections as early as previous versions,' she said.
'So if you feel any symptoms but test negative, it's not a get-out-of-jail-free card. You may need to test again and hold off a little bit on assuming that you're negative.'
However, despite the surging demand for the tests - the CDC said Tuesday that the Omicron strain's impact on the nation's Covid infections may have been overblown by as much as 50 percent.
The agency released a revised chart on Tuesday showing that the new variant accounted for 23 percent of all cases for the week ending on December 18, as opposed to the 73 percent it originally reported.
http://www.stationgossip.com/2021/12/now-fda-says-rapid-tests-for-covid.html