Mixing coronavirus vaccines without necessary data ‘a huge gamble,’ experts say

Different vaccines to protect against the novel coronavirus shouldn’t be mixed-and-matched, despite Britain’s recent decision to allow the practice to be used in rare occasions, health experts say.

Mixing different coronavirus vaccines without any data to suggest the safety and efficacy of the practice is “a huge gamble,” Dr. Colin Furness, an infection control epidemiologist and assistant professor at the University of Toronto said.

“I think it’s irresponsible … it’s unethical because we don’t know what that does,” he said. “We don’t know what the effectiveness is, we don’t know what the side effects are.”

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Dr. Isaac Bogoch, an infectious diseases faculty member at the University of Toronto said while there may be “some theoretical reasons” as to why vaccine mixing “may provide decent protection to COVID-19 infections,” the data is not yet conclusive.

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“Until we see better data to support that, I don’t think we’re going to see any such activity in Canada,” he said.

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The comments come after Britain released new guidelines on New Year’s Eve which will allow people seeking their second dose to be given shots of different COVID-19 vaccines on rare occasions.

“(If) the same vaccine is not available, or if the first product received is unknown, it is reasonable to offer one dose of the locally available product to complete the schedule,” according to the guidelines.

Mary Ramsay, head of immunizations at Public Health England, said this would only happen on extremely rare occasions, and that the government was not recommending the mixing of vaccines, which require at least two doses given several weeks apart.

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She said “every effort should be made to give them the same vaccine.

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“But where this is not possible it is better to give a second dose of another vaccine than not at all,” she said.

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What has Health Canada said?

Health Canada’s National Advisory Committee on Immunization (NACI) currently recommends that the vaccine series “be completed with the same COVID-19 vaccine product.”

“Currently, no data exists on the interchangeability of COVID-19 vaccines,” the agency’s website read.

However, according to NACI, if the vaccine used for a previous dose is “not known, or not available, attempts should be made to complete the vaccine in series with a similar type of COVID-19 vaccine (e.g. mRNA vaccine).”

“In the context of limited COVID-19 vaccine supply and the absence of evidence on interchangeability of COVID-19 vaccines, the previous dose may be counted, and the series need not be restarted,” the website read.

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The agency said “active surveillance of effectiveness and safety of this mixed schedule will be important in these individuals,” adding that “accurate recording of vaccines received will be critical.”

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According to the NACI, the agency will “continue to monitor the evidence” and will update its recommendations as needed.

To date, Health Canada has approved two coronavirus vaccines for use across the country. Both are mRNA vaccines, and require two doses to provide around 95 per cent protection from COVID-19.

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The Pfizer-BioNTech vaccine requires two shots to be administered 21 days apart, while doses of the Moderna vaccine are to be administered 28 days apart.

Bogoch said we have “good data” on these vaccines, and how they are to be administered.

Asked if there are any circumstances in which Canada should allow different vaccines to be mixed-and-matched before data is available, Bogoch said: “no.”

“I’m not entirely sure outside of a clinical trial what the role would be for conducting this type of activity,” he said.

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Furness also said vaccines should not be mixed unless in a lab setting, where participants have given their informed consent.

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“If you want to do a trial to try them out, sure,” he said. “But that’s going to take many months.”

Anything else, Furness said, would be “experimental.”

“The human history is really littered with experimenting on people without the understanding that they’re being experimented on,” he said. “And that’s really not OK.”

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For now, Bogoch said we should focus on rolling out the approved vaccines as quickly as possible, in the manner in which they are meant to be administered.

“The goal is to have as few vaccines in freezers as possible and get the needles in arms quickly as possible to the highest risk groups and prevent death and suffering,” he said.

–With files from Reuters

© 2021 Global News, a division of Corus Entertainment Inc.