Cross Country Checkup·Ask Me Anything

Mixing vaccine doses and getting the shot while pregnant: Your COVID-19 vaccine questions answered

With variants fuelling a third wave of the COVID-19 pandemic — and vaccinations rolling out across the country — many Canadians still have questions about the safety and efficacy of coronavirus vaccines.

Infectious diseases experts answer callers' questions on Checkup's Ask Me Anything

A worker waits to assist people outside at a mass COVID-19 vaccination site during the COVID-19 pandemic. More than five million COVID-19 vaccine doses have been administered in Canada as of Sunday morning. (Nathan Denette/The Canadian Press)

With variants fuelling a third wave of the COVID-19 pandemic — and vaccinations rolling out across the country — many Canadians still have questions about the safety and efficacy of coronavirus vaccines.

More than five million doses of COVID-19 vaccines have been administered in Canada as of Sunday morning.

Dr. Fatima Kakkar and Dr. Alex Wong answered callers' questions on the topic Sunday evening as part of Cross Country Checkup's regular Ask Me Anything series.

Can you mix vaccine doses?

Calling from Selwyn, Ont., Sherilyn Effer asked for clarity on whether or not it's safe to mix and match vaccines that require multiple doses.

Wong, an infectious diseases physician at Regina General Hospital and assistant professor at the University of Saskatchewan, says that ultimately all of the COVID-19 vaccines approved for use in Canada today work the same way — by triggering an immune response to create antibodies against the coronavirus spike protein.

But as it stands, there is little research to back up the mixing of vaccines between the first and second dose.

"There is definitely ongoing study in this area. But right now, there is not really real world evidence to support any of this because everybody is trying to follow the manufacturer guidance," Wong said.

"Obviously, manufacturers studied their own vaccines. They didn't study their own vaccines in combination with other people's vaccines."

With that in mind, Wong says that vaccine providers across the country aim to provide the same vaccine for both doses. However, he says that future research could show it is safe to mix and match, but he believes that's "unlikely."

"There is not clear data showing that you can mix and match appropriately, and we would not recommend it," said Wong.

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A new trial is looking into the possibility of getting different types of COVID-19 vaccines for each dose and what it could mean for the fight against COVID-19. 2:03

Are COVID-19 vaccines safe for people who are pregnant or breastfeeding?

Sarah Wells, who called from Ottawa, asked if doctors have come to a consensus about the safety of the vaccines for pregnant people. 

"The quick answer is that, yes, there's a consensus amongst doctors," said Kakkar, a pediatric infectious disease consultant at Sainte-Justine Hospital in Montreal and assistant professor at the University of Montreal.

She notes that the Society of Obstetricians and Gynaecologists of Canada released a statement saying that the vaccine is recommended for people who are pregnant. 

"There have been thousands of pregnant women through the U.K. and the U.S. who've been vaccinated without any signal of any effects on the newborn," Kakkar said. 

And while there is an absence of data from clinical trials on this topic, Kakkar says that the risks associated with COVID-19 are higher than the risks associated with the vaccine — particularly for people with diabetes, hypertension or other factors that contribute to high-risk pregnancies. 

Still, Kakkar says that pregnant people should speak with their doctors prior to getting vaccinated.

Dr. Fatima Kakkar says that people who are pregnant should speak with their doctor about COVID-19 vaccines. (Shutterstock/Bernardo Emanuell)

But what happens once the child is born?

Claire Hatch emailed from Vancouver to ask what the latest indications are for vaccinating people who are breastfeeding.

"Breastfeeding is not an exclusion or a contraindication to getting your COVID-19 vaccine," said Wong. 

He noted that there is data that suggests once you're vaccinated and have antibodies against COVID-19, you can pass that on to your newborn through breastfeeding. 

This way, "you're protecting not only yourself and your family, but also your newborn, in the process," he added.


Written by Caro Rolando and Jason Vermes. Produced by Steven Howard

Hear more from Dr. Fatima Kakkar and Dr. Alex Wong in Cross Country Checkup's Ask Me Anything on CBC Listen.

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