As Canada continues to roll out COVID-19 vaccines, at least one country is considering mixing and matching different doses.
A trial, led by Oxford University, is now underway in the United Kingdom to test the safety and efficacy of mixing different shots to protect against the novel coronavirus.
If the results are positive, experts say the practice could help ease supply chain issues and boost recipients' more robust immune responses.
So far, Health Canada has approved four vaccines to protect against COVID-19.
Two are mRNA vaccines — one from Pfizer-BioNTech and the other from Moderna.
Vaccines from Johnson & Johnson and AstraZeneca-Oxford have also been approved for use in the country.
All vaccines except the shot from Johnson & Johnson require two doses, administered some weeks apart.
Earlier this month, Health Canada’s National Advisory Committee on Immunization (NACI), recommended that provinces and territories wait up to four months to administer the second dose to their citizens in order to vaccinate as many people as possible as Canada faced down significant supply shortages.
Canada is currently relying solely on vaccines shipped to the country from international partners. Because of this, the country has faced a number of delays that have severely hampered its mass vaccination plan.
Most recently, on Thursday, Canada’s Procurement Minister, Anita Anand, said Canada’s shipment of Moderna vaccines would be delayed a few days, citing a “backlog” in the company’s quality assurance process.
“The 590,000 doses that were due to arrive in Canada this weekend have been delayed by a few days,” Anand said in a statement posted to Twitter.
She said they will arrive in Canada “no later than Thursday” of this week.
Is vaccine mixing safe?
Dr. Isaac Bogoch, an infectious diseases faculty member at the University of Toronto, said that based on the data we have right now, we shouldn’t be mixing COVID-19 vaccines.
“The U.K. is conducting these clinical trials now,” Bogoch said, adding that it will be “extremely helpful” when we have the data to analyze.
Bogoch said we will have “much more clarity on the safety, but also the efficacy” of vaccine mixing in the coming months.
He said ultimately it’s a “smart idea,” and could prove to be helpful if there is a scarcity of one type of vaccine.
“Perhaps there will be evidence demonstrating that you can use another vaccine as the second dose,” he said.
Bogoch said there are also “theoretical benefits that you can mount a more robust immune response” by using two different vaccines.
“There are theoretical reasons why you want to do this, but we don’t yet have that data available,” he said. “So I don’t think we’re going to we’re going to see that done.”
Dr. Alan Bernstein CEO of the Canadian Institute for Advanced Research echoed Bogoch’s remarks saying “each of the vaccines have different characteristics in terms of how and what they boost in our immune system.”
He told Global News with a mix and match strategy, we could see a “kind of synergy between the two different vaccines” that we wouldn’t otherwise get with a single vaccine strategy.
Bernstein said, though, that for now, that’s “all on paper.”
“And that’s why this trial so important,” he said.
What has the government said?
NACI still recommends a person’s vaccine series “be completed with the same COVID-19 vaccine product.”
That means both doses should be from the same manufacturer.
“Currently, no data exist on the interchangeability of COVID-19 vaccines,” the committee’s website reads.
However, NACI said, “if the vaccine product used for a previously received dose is not known, or not available, attempts should be made to complete the vaccine series with a similar type of COVID-19 vaccine (e.g., mRNA vaccine and mRNA vaccine).”
The committee said it “is not recommended that vaccines of different types (e.g., mRNA vaccine and viral vector vaccine) be used in the same series.”
“In the context of limited COVID-19 vaccine supply and the absence of evidence on the interchangeability of COVID-19 vaccines, the previous dose may be counted, and the series need not be restarted,” the agency’s website reads.
NACI said, “active surveillance of effectiveness and safety of a mixed schedule will be important.”
The committee said its recommendations regarding the mixing of doses may change as more evidence becomes available.
Health Canada told Global News an application to hold a trial to test the efficacy and safety of COVID-19 vaccine mixing has not yet been submitted.
From Global News’ Crystal Goomansingh
