Vaccinated Canadians can have COVID-19 symptoms despite testing negative. Here’s why – National | Globalnews.ca


As Canada heads in direction of a sixth wave of COVID-19 with rising circumstances and hospitalizations throughout the nation, consultants say folks can nonetheless check destructive on a rapid test within the first few days they’ve signs.

That is partly attributable to how shortly vaccination clears the quantity of the virus in an contaminated individual’s physique.

“If the antigen check depends on the quantity of virus in your higher respiratory tract, you’ll nonetheless be infectious … within the first few days,” mentioned Dr. Earl Rubin, an infectious illness specialist and a division director of pediatric infectious ailments on the Montreal Kids’s Hospital.

“However you might clear the virus extra quickly if in case you have good antibody from the vaccine … and due to this fact the antigen check could change into destructive faster in those that are vaccinated slightly than the unvaccinated,” he added.

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Rubin explains that how shortly a vaccinated individual clears the virus doesn’t essentially imply that speedy antigen exams aren’t working.

“Antigen exams can be found and (they’re) quick … You don’t have to depart your home, you are able to do it your self. So there are a number of benefits, however I believe folks have to actually perceive the restrictions of the exams,” he mentioned.

Rubin provides there’s a debate amongst well being consultants on whether or not antigen exams is probably not as delicate to the newer variants of COVID-19, like Omicron.

“It’s arduous to match in actual time … as a result of antigen exams weren’t as available or used as a lot as they’re now, however they actually do work,” he mentioned.


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In February 2022, the Ontario COVID-19 Science Advisory Desk published findings from an evaluation of preprint research suggesting that the pooled sensitivity of speedy antigen exams for detecting Omicron infections is about 37 per cent, in comparison with 81 per cent for the Delta variant.

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Well being Canada says on its website that it has “no evidence” that variants have an effect on the power of agency-approved exams to substantiate COVID-19 circumstances, however notes that these new units are nonetheless being investigated.

“All exams have a capability to point out a false constructive and a false destructive,” mentioned Tim Sly, an epidemiologist and professor emeritus within the Faculty of Public Well being at Ryerson College.

“There’s a interval of round two days earlier than the speedy check begins to select up the antigen … as a result of bear in mind, it’s on the lookout for the protein and there’s obtained to be sufficient of the protein there,” he added.

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Sly says that by the third day, a speedy check would have the ability to decide up the antigen that’s replicating within the physique.

“That is one cause why it’s at all times good to present a second speedy check, a day or two afterward, simply to verify it’s actually destructive.”

Sly explains that the quantity of immunity an individual has constructed up, how a lot of the virus an individual can unfold to others and the way critical an individual’s illness is, are all depending on the viral load, which is the quantity of virus an individual has of their system.

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Rubin says antigen speedy exams decide up on the next viral load a lot faster.

“The antigen check could be very a lot depending on what we name the viral load, and that’s very a lot depending on the stage of the sickness that you just’re in,” he mentioned.

Nonetheless, the “actual drawback” from an epidemiological perspective, mentioned Sly, is that between 40 to 70 per cent of people that carry COVID-19 wouldn’t have any signs in any respect.

“You don’t really know who’s virus-positive strolling round. It may very well be the individual sitting subsequent to you on the bus. They could be shedding the virus each time they open their mouths … and also you don’t comprehend it,” Sly mentioned.

“So this has induced an incredible quantity of an issue. And sure, a few of these folks will go on to develop the sickness a bit afterward, and a few by no means do. This is among the many elements of this virus that’s been an actual drawback, an actual headache,” he added.

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This implies people who find themselves carriers of the virus is probably not getting examined in any respect as a result of they don’t have any signs and don’t assume they’ve COVID-19; in the event that they do occur to get examined, it’s typically destructive.

Sly says these folks ought to proceed to do a number of exams to verify they’re COVID-free.

Thus far, the government of Canada said on its website that testing has relied on molecular testing (PCR) collected by a health-care skilled and that it stays the gold commonplace for testing.

A speedy check, nevertheless, is “pretty much as good as a coin toss,” based on Rubin, particularly on the primary day of testing.

“If a speedy antigen check is constructive, it’s dependable. If it’s not constructive and you’ve got signs suitable with COVID, you ought to be managing your self and the folks round you as if you’re COVID-positive,” mentioned Rubin.

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– with information from The Canadian Press

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