Can vaccinated people spread COVID-19? Data too limited, Health Canada says

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It is still too early to say with any amount of certainty whether vaccines prevent people from spreading COVID-19 to others who are not yet vaccinated, Health Canada says.

The statement from officials comes after The New York Times reported on Thursday that the U.S. Centers for Disease Control and Prevention (CDC) was walking back comments by its director.

Dr. Rochelle Walensky said earlier in the week that vaccinated people did not become infected or spread the virus to others — something that quickly prompted criticism from infectious disease experts who stressed there is simply no data to prove that.

“While COVID-19 vaccines authorized in Canada have demonstrated efficacy against symptomatic illness, hospitalization and death, there were only limited data on their ability to prevent asymptomatic infection or to prevent transmission to others,” said André Gagnon, spokesperson for Health Canada, in an email.

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“While the Department is aware of this study, until there is more evidence, continuing adherence to public health measures to protect those around you remains necessary.”

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Gagnon referred to the study released on March 29 by the CDC that Walensky cited in her comments.

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She had said that the data “suggests that vaccinated people do not carry the virus, don’t get sick.”

Scientists quickly pointed out though that the data did not specifically say that.

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Instead, the data found that one dose of either the Moderna or Pfizer vaccines was 80 per cent effective at preventing the person who got the shot from being infected with COVID-19, while two doses appeared to be 90 per cent effective at preventing the person from becoming infected.

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Critics noted that suggests that while the risk of a vaccinated person spreading the virus to unvaccinated people appears low, it’s not non-existent — which is why experts continue to advise fully vaccinated people to keep practicing physical distancing and masking around others who are not vaccinated.

“Dr. Walensky spoke broadly during this interview,” the newspaper quoted a CDC spokesperson as telling their reporter when asked about the director’s comments.

“It’s possible that some people who are fully vaccinated could get COVID-19. The evidence isn’t clear whether they can spread the virus to others. We are continuing to evaluate the evidence.”

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Colin Furness, an epidemiologist at the University of Toronto’s Dalla Lana School of Public Health, said the challenge for public health experts lies in the need to be cautious about a lack of clear data.

“That’s enormously difficult to measure. You’d have to take vaccinated people – a very, very large number of them, and then swab their noses every day for a very long period of time. That would be the only way to know,” he said when asked about the evidence available so far.

“I don’t think that’s been done.”

Furness said given the uncertainty that remains, Walensky’s comment may have been “irresponsible” in that it could encourage vaccinated people to take risks where they could still infect others.

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“She might be saying there is no evidence that they do [spread the virus],” Furness added. “But an absence of evidence is not evidence of absence.”
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–With files from Global News’ Linda Boyle

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