Nasal swab tests slower at detecting Omicron infections; Expert

By Amirtha P S, Desk Reporter
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According to an infectious disease expert, swabbing the nose with a rapid antigen test will not reliably detect the Omicron variant in the first few days of infection, so to enable manufacturers to safely collect samples from the throat they must seek US approval.

The US Food and Drug Administration (FDA) has expressed concerns over the safety of self throat swabbing. Dr. Michael Mina, Chief Science Officer at eMed, stated that people can transmit Omicron to others when it has infected their throat and saliva but before the virus reaches their nose, so swabbing the nostrils too early in the course of infection will not pick it up.

According to the study released on medRxiv ahead of peer review, looked at 29 Omicron-infected workers in high-risk professions who had PCR and antigen tests done simultaneously on multiple days. The PCR tests of saliva detected the virus on average three days before the rapid nose-swab samples became positive.

“When people test negative by rapid antigen, they can still have very infectious viral loads and transmit to other people,” said study leader Dr. Blythe Adamson of New York-based risk reduction company Infectious Economics.

Some experts have advised antigen-test users to swab the throat before swabbing the nose. The FDA, however, said users should follow manufacturers’ instructions. The agency said there are safety concerns regarding self-collection of throat swabs, “as they are more complicated than nasal swabs, and if used incorrectly, can cause harm to the patient.”

“The CDC recommends that throat swabs be collected by a trained healthcare provider,” the FDA said. Before the FDA would approve at-home throat swabbing, manufacturers would need to conduct studies to show that consumers could safely perform the tests, and provide detailed instructions with each test kit, Dr. Mina said.

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