Antigen tests appear less sensitive to Omicron variant, US agency warns

Antigen tests appear less sensitive to Omicron variant, US agency warns
Credit: Belga

Rapid antigen tests may not be able to detect an infection with the Omicron variant as succesfully, as they appear to be less sensitive to it than to other mutations, the United States’ medicines watchdog warned.

These particular tests, which are advantageous due to their ability to be used at home and to provide quick test results, do detect the Omicron variant, but “may have reduced sensitivity” compared to PCR tests, the Food and Drug Administration (FDA) stated in a preliminary warning on its website on Tuesday. 

This could mean that there is a greater chance of antigen tests providing a negative result even though a person is infected with the particular variant, which has more mutations than any previous Covid-19 strain.

However, although the preliminary study, analysing the performance of antigen tests with patient samples that were infected with the Omicron variant, is the best way to evaluate true test performance in the short-term, the FDA stressed that the laboratory data does not replace clinical study evaluations with live virus, which are still ongoing.

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The FDA will still allow the use of antigen tests at the moment, “in accordance with the instructions included with the tests,” but added that if a person tests negative with an antigen test but is suspected of having Covid-19, follow-up PCR testing is important for determining an infection.

Early data suggests reduced risk

The Omicron variant of the coronavirus is continuing its rapid spread. Almost one month ago, the variant accounted for just 0.3% of all cases, but as of Monday, it accounts for 60% of confirmed cases in Belgium. Last weekend, Omicron overtook Delta to become the dominant variant in the country.

Although more data is needed on the new strain, particularly when it comes to the current vaccines’ protection against hospitalisation and death following an infection with the variant, a British study carried out by the UK Health Security Agency (UKHSA) showed it less often leads to severe illness and hospitalisation than previous strains.

The World Health Organisation (WHO) stated on Wednesday that early data from South Africa and Denmark also suggests there is a reduced risk of hospitalisation for the Omicron compared to the Delta variant, but stressed that further data are needed to understand the clinical markers of severity.

It warned that the overall risk related to the new variant of concern Omicron “remains very high,” as the number of cases reported globally increased by 11% since last week.

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