This means that they can give false negative results even if someone is infected with Omicron variant.

Antigen tests for SARS-CoV-2, which have the great advantage of being effective within minutes, are less sensitive to the Omicron variant than previous ones, US health authorities warned on Tuesday.

This means that tests of this kind may give false-negative results, even if someone has been infected with Omicron.

“Early data suggests that antigen tests do detect the Omicron variant but may have reduced sensitivity,” said a statement from the US Federal Drug Administration (FDA).

“if a person tests negative with an antigen test but is suspected of having Covid-19, such as experiencing symptoms or have a high likelihood of infection due to exposure, follow-up molecular testing is important for determining a Covid-19 infection,” the agency stated.

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, due to the rapid rise in infections attributed mainly to Omicron and 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.

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