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.
"Preliminary data suggests that antigenic tests detect the Omicron variant well, but with reduced sensitivity," the US Medicines Agency (FDA) said in a statement.
However, she specified that she would continue to authorize their use, following the precise instructions for use.
"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 ( or PCR, editor's note) is important, ”said the agency.
Antigen tests detect antigens on the surface of the virus, while PCR tests look for the genetic material of the virus.
The first were already less sensitive than the second, recalls the FDA.
And their sensitivity is now affected due to the many 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 take-home rapid tests, which can be ordered by Americans through a dedicated website, starting in January.
© 2021 AFP