Rapid test using a nasal swab does not reliably detect the Omicron variant of the new coronavirus within the first few days of an infection, so manufacturers in the US should seek approval to allow users to collect safely sample from the pharynx, according to an American infectious disease specialist.
The US Food and Drug Administration (FDA) has expressed concern about the safety of pharyngeal sampling without the supervision of a specialist.
“Carriers can transmit Omicron when the pharynx and saliva are infected, before the virus even reaches the nose, so taking a sample from the nose while it is still too early will not detect the infection,” Dr. said in a press conference. Michael Mina, a former professor at Harvard School of Public Health and now a senior fellow at eMed.
A study published Wednesday in medRxiv analyzes the cases of 29 “high-risk” workers infected with the Omicron variant who underwent PCR and antigen testing at different dates. Molecular tests (PCR) detected the virus on average three days before rapid nasal sampling tests were positive.
“While some people are negative for rapid antigen testing, they may already have a high viral load and pass it on to others,” said Blitz Adamson, chief research officer at Infectious Economics LLC, based in New York.
A positive antigen test is very reliable, notes Mr. Mina and advises: “When you have symptoms, assume you are positive”, but wait to do the antigen test after a few days. Rapid tests “detect Omicron fine” when it has reached the nose, he explained.
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