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Mixing, matching COVID-19 vaccines is safe, reasonable, say experts

Last Updated Jun 2, 2021 at 11:48 am MDT

Two vials of the Pfizer-BioNTech vaccine sit on a table at a COVID-19 vaccination clinic in Halifax on Monday, May 24, 2021. THE CANADIAN PRESS/Andrew Vaughan

Expert says some countries have been giving people different vaccines for their second doses for months

Infectious diseases expert says all vaccines give your body the same information to create antibodies

B.C. set to unveil its vaccine mixing and matching plan on Thursday

VANCOUVER (NEWS 1130) – Alberta is expected to follow updated guidelines from Canada’s vaccine panel, which said you can mix and match COVID-19 vaccines if required.

Federal health officials announced the update on Tuesday, saying a second shot of an mRNA vaccine, like Moderna or Pfizer, can be the follow-up to a first dose of AstraZeneca.

The National Advisory Committee on Immunization also said if you had an mRNA shot as your first dose, you should be given an mRNA as your second, although it doesn’t matter if it’s Pfizer or Moderna, suggesting the two are interchangeable.

This is a move some countries have already adopted, according to Dr. Isaac Bogoch, an infectious disease expert out of Toronto General Hospital.

“This is largely based on studies that have come out of Spain and the United Kingdom. Some are looking at safety, some are looking at the immune response. I think it’s also fair to say France and Germany have been mixing and matching vaccines for at least a couple of months now. They were giving second doses of mRNA vaccines and there haven’t been any safety signals coming out of those countries,” he explained.

Horacio Bach, an infectious disease expert at UBC, says while two major studies on mixing and matching are only using a few hundred participants, there have been no issues.

“The two studies that we know from the U.K. and Spain show that it can be done. There’s no severe symptoms,” he said.

He notes all vaccines give your body the same information to create antibodies — the only difference between the shots is how the drug is delivered in the body.

“For example, in the Moderna and Pfizer, you use the mRNA … that gives instruction to your cells to produce the protein of the virus using genetic material, like RNA. In the case of AstraZeneca, we use what is called a harmless virus, and the virus has the protein express on the surface. So that is a virus that doesn’t do anything, basically,” Bach explained.

“But the protein we use in order to prime or stimulate our body, is the same.”

He suggests concerns using Pfizer or Moderna as a second dose are much lower compared to AstraZeneca as second dose.

“Because it’s only the mRNA that once it’s inside the cell, is destroyed. So there’s no part of the protein, of the virus, circulating in the body.”

And while some people may still have concerns, Bogoch notes the idea of mixing and matching vaccines isn’t new.

“To put it into context, you know, we have been mixing and matching vaccines for long before COVID-19 was even known,” he told NEWS 1130.

“It sounds like a very reasonable plan. We know that some people who’ve had a first dose of AstraZeneca are pretty keen and want a second dose of AstraZeneca, and I think it’s fair that they are given that option. We also know some people who don’t want a second dose of AstraZeneca and would prefer to get a second dose of one of the mRNA vaccines. And I think that’s also fair and reasonable that we give people that option,” Bogoch added.

He stresses the key is to help and enable people to make their own informed decisions, and “discuss what the pros and cons of each approach might be and really contextualize it for the individual.”

More than 60 per cent of eligible Canadians have received at least one dose of a COVID-19 vaccine so far, according to Canada’s top health officials.

The latest modelling showed deaths and cases of the virus are dropping significantly across the country, and that we’re over the peak of the third wave.

Hospitalizations and ICU admissions are also seeing a decline, with health officials adding that vaccine administration was continuing to ramp up.

However, Canadians continue to be asked to remain vigilant, with many of the provinces already lifting restrictions.