Manitoba vaccine lead says mixing vaccines is part of pandemic's 'big human experiment'

Dr. Joss Reimer, medical lead, Manitoba Vaccine Implementation Task Force, speaks about COVID-19 vaccination initiatives and answers media questions during a COVID-19 live-streamed press conference at the Manitoba legislature in Winnipeg Wednesday, March 17, 2020. THE CANADIAN PRESS/John Woods

Dr. Joss Reimer, medical lead for Manitoba’s Vaccine Implementation Task Force, says that new vaccine recommendations from the National Advisory Committee on Immunization on mixing mRNA vaccines will be a form of trial and error.

“Well in some ways, during a pandemic everything we do is a big human experiment,” she said in an interview with CTV’s Question Period airing Sunday. “Because we're all having to learn together at the same time, about what works the best.”

On Tuesday, NACI changed its guidelines to allow for Canadians to mix and match AstraZeneca with either mRNA vaccine from Moderna or Pfizer. There was no current data on the interchangeability of mRNA vaccines.

Chief Public Health Officer Dr. Theresa Tam says NACI still recommends sticking with the same mRNA vaccine regime for both doses, but that you can mix if there are problems with availability.

“People who received the first dose of an mRNA vaccine, so that's Pfizer-BioNTech or Moderna vaccines, should be offered the same mRNA vaccine for the second dose,” she said during a briefing on Tuesday.

NACI said in a statement there is no reason to believe that using a different mRNA vaccine for your second dose would result in any additional safety concerns.

Reimer says that mixing and matching vaccines is a not a new practice in the medical field.

“We have a lot of experience doing this in the past,” said Reimer. “And what these small trials did is reassure us that it doesn't look like the COVID vaccines will be different than our previous experience.”

There are currently two studies on mixing COVID-19 vaccines, both in Spain and the United Kingdom, whose preliminary results indicate that mixing and matching the AstraZeneca and Pfizer vaccines is safe.