In the event of symptoms or a high risk of exposure, a negative result should therefore be confirmed by a PCR test.
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They have the advantage of delivering a result in just a few minutes, but with caution. Antigenic tests for Covid-19 are less sensitive to the Omicron variant than to previous variants, warned US health authorities on Tuesday, December 29. This means that these tests are more likely to indicate a negative result despite an infection – the notorious false negatives – if a person is infected with Omicron. These tests have the advantage
“Preliminary data suggests that antigen tests detect the Omicron variant well, but with reduced sensitivity”, said in a statement (in English) the United States Drug Administration (FDA). Their use remains authorized, but with some precautions. “If a person tests negative with an antigen test, but is suspected of having Covid-19, for example having symptoms or a high probability of infection from exposure, follow-up with a molecular test [PCR] is important”, stressed the agency.
Antigen tests detect antigens on the surface of the virus, while PCR tests look for the genetic material of the virus. The former were already less sensitive than the latter, recalls the FDA, and their sensitivity is now affected due to the numerous mutations of the Omicron variant. Even so, antigen tests, sometimes called rapid tests, are widely promoted by experts because they can be done regularly at home for little cost and thus help control the epidemic.
In the United States, these increasingly popular home test kits have recently come to an end with the very sharp rise in contamination linked to Omicron and with the end of the year celebrations. Last week, President Joe Biden announced the purchase of 500 million rapid home tests, which can be ordered by Americans through a dedicated website, starting in January. In France, supermarkets will be able to sell self-tests for a month.