Antigen tests have reduced sensitivity to omicron variant - US FDA

Wena Cos, ABS-CBN News

Posted at Dec 29 2021 12:54 PM | Updated as of Dec 30 2021 03:27 PM

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MANILA - Rapid antigen tests have reduced sensitivity in detecting the more transmissible omicron COVID-19 variant, said the US Food and Drug Administration (FDA), citing early data based on laboratory studies.

The FDA partnered with the US National Institute of Health's RADx program to test patient samples containing the live virus, presently existing omicron variant in patients, and found that "antigen tests do detect the omicron variant but may have reduced sensitivity."

Tests were previously done on rapid antigen tests with 'heat-inactivated' omicron variant samples, which are samples of the virus that are no longer live. 

The tests with the heat-treated samples proved that rapid antigen tests detect the omicron variant with similar effectivity as other previously identified variants.

The FDA said that live samples of the virus are 'the best way to evaluate true test performance in the short-term.'

However, preliminary results from laboratory data are not sufficient enough to replace clinical studies done with patients with live virus samples, more of which are presently done.

The FDA recommended the continued use of rapid antigen tests is authorized. 

The Department of Health in September released an evidence report that recommends rapid antigen tests be used to initiate contact tracing, surveillance, and clinical management for suspected and probable cases of COVID-19.

Probable cases include individuals who have been in contact with a probable or confirmed COVID-19 case, and those with an onset of anosmia and ageusia or the loss of smell and taste. 

Suspect cases are those who have an onset of flu-like symptoms, individuals who reside and/or work in areas with high-risk transmission, and those who reside or have traveled in areas with community transmission. 

Rapid antigen tests are also allowed for targeted screening in presumptive outbreaks where RT-PCR test results of a suspect case are not yet available.

The health department also allows its use for local border screening, and international border screening.

On Thursday, the DOH said that it will not change its guidelines on the use of tests, despite the recent study released by the US FDA. 

"As of this time, there is no reason to change our guidelines on the use of antigen tests as these have been crafted with the previously stated context in mind," the health department said.

It reminded that rapid antigen tests are best used for individuals who are symptomatic or have high risk of exposure. 

A negative antigen test should be supplemented with an RT-PCR test after days 3-5, if with symptoms or exposure, to conclusively know an individual's status.

The health department emphasized that "tests need to be used the right way, at the right time as part of an entire system of interventions."