The antigen tests for SARS-CoV-2, which have the great advantage of giving results in a few minutes, are less sensitive to the Omicron variant than in previous ones, the US health authorities warned on Tuesday.
This means that tests of this kind are likely to give false negative results, even if someone has been infected with Omicron.
"Preliminary data suggest that antigen tests do detect the Omicron variant, but have reduced sensitivity," said a statement from the US Federal Drug Administration (FDA).
However, he noted that he continues to recommend their use, in compliance with the instructions for use.
"If someone gets a negative result after taking an antigen test, but there are suspicions that he has been infected (…), for example if he has symptoms (of COVID-19"or a high probability of infection due to exposure, it is important to do a molecular test (s.s. PCR test)," said the organization.
Antigen tests look for antigens on the surface of the virus; molecular tests look for its genetic material. The former were already less sensitive than the latter, the FDA recalled.
The sensitivity of these tests is further reduced due to the multiple mutations of the Omicron variant.
Nevertheless, antigen tests, also known as rapid tests, are considered useful by experts in general, as they can be performed frequently, at home, at low cost, helping to control the pandemic.
In the US, home screening kits, which are becoming increasingly popular, are now running out, in part due to the rapid rise in infections attributed mainly to Omicron and in part due to the end-of-year holidays.
Last week, President Joe Biden announced the purchase of 500 million quick home tests. Americans will be able to order them through a special website that will be operational from January.
Source: RES-EAP