Covid: antigen tests less effective to detect Omicron, according to American health authorities

Published by Manon C. · Published on 29 December 2021 at 15h57
As the Omicron variant dominates in several countries across the world, are PCR and antigen tests likely to detect this new variant? According to the U.S. health authorities, antigen tests are less sensitive to Omicron.

As the swift spread of the Omicron variant worries the World Health Organization, as well as pharmaceutical laboratories, and while the fifth Covid wave is raging in France with an always growing incidence rate and many new daily contaminations, the question is: are PCR and antigen tests effective to detect the Omicron variant?

This Tuesday December 28, 2021, the U.S. Food and Drug Administration (FDA) has stated antigen tests deliver a negative result most of the time despite infection with Omicron. In otherwords, these "false negative" are caused by tests less sensitive to Omicron than the previous variants.

"Early data suggests that antigen tests do detect the omicron variant but may have reduced sensitivity. [...] 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 U.S. authorities claim.

For the record, this past November 28, 2021, the World Health Organization announced: “The widely used PCR tests continue to detect infection, including infection with Omicron”. But when it comes to antigen tests, the WHO chose to be cautious specifying: “Studies are ongoing to determine whether there is any impact on other types of tests, including rapid antigen detection tests”. They go on: “At the present time, WHO is coordinating with a large number of researchers around the world to better understand Omicron. Studies currently underway or underway shortly include assessments of transmissibility, severity of infection (including symptoms), performance of vaccines and diagnostic tests, and effectiveness of treatments”.

The news has been confirmed by the Health General Board stating in a report issued on November 27 to all health professionals: “To date, the B.1.1.529 variant (Omicron) can only be confirmed through sequencing”. A report shared by the Health minister who recommends to guide “anyone who stayed in countries at risk regarding the B.1.1.529 variant in the past 14 days or who have been in touch with someone who stayed to perform a RT-PCR test (including if they are coming for an antigen test)”.

Unlike the nasopharyngeal PCR test swabs – likely to detect the nature of the variant that caused infection – antigen tests (less deep nose swabs) shall be subject to “screening” test in the event the test is positive to determine the nature of the virus.

Therefore, it seems so far PCR tests are to be opted for rather than antigen tests and self-tests.

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