Friday, May 20, 2022

Why double-vaccinated people in some places are testing positive for COVID more often than unvaccinated

‘The first thing that comes to my mind is that I see no biological explanation for this’

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As one infectious disease expert put it, the trend is “curious.”

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Recently in at least three provinces, Canadians who are double-vaccinated are more likely to test positive for COVID than those without, a fact that has been seized upon by anti-vaccination activists because Supposedly the shots don’t work.

In Alberta, for example, on Monday, 89 out of 100,000 people who received two doses of the vaccine tested positive for the coronavirus, compared with 68 in 100,000 of those who had avoided vaccination so far.

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But experts say the trend probably stems from statistical “bias” – the nature of people who have been tested and who were frequently exposed to the virus – and certainly not some strange quirk of vaccination.

In short, they suggest that people who have been vaccinated are more likely to seek PCR testing for employment and other reasons – and more apt to be exposed to COVID, skewed the data. Do because the Omicron version spreads fast.

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“It’s curious,” admits Dr. Mark Loeb, an infectious disease physician and professor at McMaster University. “For me the first thing that comes to mind, I don’t see any biological explanation for this. I don’t think it makes sense.”

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The “confounding” trend can be explained logically, but “it behooves us not to hide or minimize these data, but to wrestle with them,” says University of Ottawa epidemiologist Revat. Devanandan says.

Meanwhile, the numbers clearly show that unvaccinated Canadians are still more likely to develop severe COVID disease that landed them in a hospital or an intensive care unit.

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And in one province where data is available, people who received a booster dose, a third, have a lower rate than those who tested positive. What’s more, the current trend is a short-term anomaly; For example, data from Alberta shows that during the past year, about 58 percent of cases were unvaccinated or people were diagnosed soon after their first dose—a minority group for months now.

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Still, as a small number of Canadians builds up their resistance to COVID vaccination, the plethora of pandemic-related data released by federal and provincial governments is being closely watched.

And some of it is not what is to be expected.

Similar to Alberta’s experience, Ministry of Health figures in Ontario show that on January 24, 41 out of every 100,000 double-vaccinated residents tested positive for COVID-19, compared with 39 non-vaccinated and 27 receiving a single dose. Was found

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BC In the U.S., the rate of double-vaccinations per 100,000 reached 71 on 5 January, while 53 were non-vaccinated. Since then, however, double-vaccination has led to positive testing at a lower rate than non-vaccination.

In all cases, the trend began in late December as Omicron began to take hold and the virus spread more easily and widely – months after most were most likely to test positive without vaccination.

It has been well established that vaccines provide less protection against infection from omicrons than previous iterations of SARS-CoV-2, although they are still potent in fighting severe disease. And the absolute number of vaccinated people is about 10 times higher than unvaccinated.

But why double-vaccinated can now test positive at higher levels per person Rate Compared to the non-immune? Or as Devanandan writes in his “devanandiya” blog, “WTF is going on here?”

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Experts say there is no data yet to conclusively explain this phenomenon, but there are some plausible theories.

Like other experts, Devanandan said it is telling that the trend began as Omicron took over and the virus spread at an exponential rate. He said the ability to conduct PCR tests was quickly eroded, with some provinces advising people with mild symptoms to avoid assessment centres, and that available spaces were “substantially reserved” for health care and other essential workers , They said.

He wrote of those employees, “the chances of them getting vaccinated are very high,” partly because some need to test negative to remain in their jobs.

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And previous research on other diseases suggests it’s likely that people already vaccinated are more inclined to get tested when they fall ill, said Dr. Ontario’s scientific director of the COVID Science-Advisory Table. Peter Juni said.

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“It’s their health care-seeking behavior,” he said. “People who get vaccinated are more likely to have access to health care.”

Loeb agreed, adding that a large proportion of vaccinations are almost certainly the reason for seeking testing in the first place.

But there’s probably another confounding factor as well, experts say.

Unless provinces implemented new lockdowns after the introduction of the Omicron version, those vaccinated were putting themselves at greater risk of exposure to the virus, Juni said. That’s because his status has allowed him to attend restaurants, gyms and theaters that require a vaccine passport.

“This was not a problem in the pre-Omicron era, when the Delta and previous variants were well controlled with distancing, capacity limits and casual mask wearing,” Devnandan wrote. “But Omicron changed all that. The vaccinated are now almost as vulnerable to being infected with Omicron (though much less severely).

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Nation World News Desk
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