Study casts doubts on rapid Covid tests’ reliability right after infection

A new research raises vital doubts about whether or not at-home fast antigen checks can detect the Omicron variant earlier than contaminated individuals can transmit the virus to others.

The study looks at 30 people from settings together with Broadway theaters and workplaces in New York and San Francisco the place some staff weren’t solely being examined every day however had been, due to guidelines at their workplaces, receiving each the antigen checks and a every day check that used the polymerase chain response, or PCR, which is believed to be extra dependable.

On days 0 and 1 following a optimistic PCR check, all the antigen checks used produced false-negative outcomes, though in 28 of the 30 circumstances, ranges of virus detected by the PCR check had been excessive sufficient to contaminate different individuals. In 4 circumstances, researchers had been capable of verify that contaminated individuals transmitted the virus to others through the interval earlier than that they had a optimistic outcome on the fast antigen check.

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“I feel that with each new variant that comes, scientists need to query whether or not the issues that had been beforehand true are nonetheless true,” mentioned Blythe Adamson, the lead creator of the paper and the principal epidemiologist at Infectious Economics in New York. “This one has a distinct means it travels, a distinct mechanism of motion of signs, it has completely different home windows of transmission.”

Adamson, who can be an worker of Flatiron Well being, a unit of Roche, mentioned that it was additionally attainable there have been extra circumstances of transmission than the authors had been capable of verify.

“It’s completely possible there have been many greater than 4 transmissions,” Adamson mentioned. “We named 4 as a result of there have been 4 that had been confirmed via contact tracing and epidemiology investigation. There have been possible many extra.”

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The research included each the Abbott BinaxNOW and Quidel QuickVue fast antigen checks, each of that are licensed by the Meals and Drug Administration.

The outcomes had been revealed in a preprint, which means they haven’t but been reviewed by exterior researchers.

Different information from the group point out that viral masses peaked in saliva one to 2 days earlier than they peaked in checks taken from nasal swabs, including to proof that swabs taken from the mouth or throat could detect the SARS-CoV-2 that causes Covid higher than the nasal swabs used for a lot of PCR and antigen checks.

“This group of specialists who’ve been doing sequential testing is elevating the uncomfortable risk that antigen testing is lacking individuals that may infect others,” mentioned Harlan Krumholz, director of the Middle for Outcomes Analysis and Analysis at Yale. “They’re utilizing state-of-the-art strategies and sound epidemiologic approaches leveraging a well-designed occupational well being program.”

Whereas he was not concerned within the analysis, Krumholz is thanked in acknowledgements part of the paper.

Regardless of its small measurement, the leads to the research are remarkably constant. Not a single fast antigen check detected the virus till practically two days after the preliminary optimistic PCR outcome. Moreover, the circumstances of an infection from individuals who had obtained false unfavorable outcomes might elevate alarm bells.

Nonetheless, the researchers emphasize, this doesn’t imply that fast antigen checks should not helpful. The checks additionally detected the virus in each case – it simply took longer than with PCR. So whereas the checks could not work as an early warning, a optimistic check outcome at residence does possible imply that the individual taking the check has Covid-19.

Anne Wyllie, a researcher on the Yale Faculty of Public Well being and a co-author on the paper, mentioned that the stories she is seeing from most people on social media additionally elevate her degree of concern.

“If most people is seeing this and reporting on it, you realize, that is additionally a whole lot of proof for me,” Wyllie mentioned. “Like they’re really seeing it. It is a lot extra widespread than simply this one outbreak that we had been observing.”

In the course of the pandemic, Adamson and Infectious Economics grew to become consultants to many Broadway productions that had been making an attempt to maintain their staffs secure from Covid. The chance to audiences was comparatively simple to manage, however solid and crew members labored in cramped quarters the place a lot of security precautions, together with vaccination, masking, and the usage of fast checks had been all essential to hold individuals secure.

She mentioned that as quickly as Omicron hit, there have been anecdotes about fast antigen checks remaining unfavorable till days after the contaminated individuals had already developed signs. She mentioned she began to really feel nervousness about whether or not precautions to maintain solid members secure could be sufficient. Since then, quite a few Broadway reveals, including “Waitress” and “Jagged Little Pill,” have introduced Covid-related closures.