Health·CBC Explains

What the World Health Organization really said about mixing COVID-19 vaccines

WHO's chief scientist clarifies that public health agencies are equipped to make evidence-based decisions about mixing different vaccines but individual citizens shouldn't.

Canada's vaccination program is sound, experts say after WHO remarks were taken out of context

A pharmacist draws up a dose behind vials of both Pfizer-BioNTech and AstraZeneca-Oxford vaccines on the counter. (Nathan Denette/The Canadian Press)

The World Health Organization is clarifying statements its chief scientist made on the safety and effectiveness of mixing and matching COVID-19 vaccines, after comments at a media briefing were taken out of context and caused confusion.

Canadian experts have emphasized that the remarks by WHO officials were not about Canada's COVID-19 vaccination program nor did they contradict recommendations by the National Advisory Committee on Immunization (NACI) and the Public Health Agency of Canada (PHAC). 

What happened?

At a media briefing Monday, Dr. Soumya Swaminathan, WHO's chief scientist, was answering a reporter's question about whether or not there is a need for potential third doses — or booster shots — of COVID-19 vaccines. 

The question came in the wake of Pfizer's announcement that it was seeking approval from the U.S. Food and Drug Administration to make third doses. 

As part of a lengthy response, Swaminathan warned against individuals deciding for themselves whether or not they need extra doses. 

"There is a tendency now for people in countries with enough availability of vaccines to, you know, voluntarily start thinking about an additional dose," she said. 

"It's a little bit of a dangerous trend here where people are in a ... data-free, evidence-free zone as far as a mix and match," she said. "It will be a chaotic situation in countries if citizens start, you know, deciding when and who should be taking a second, or a third or a fourth dose."

But the headline that emerged in a short story by wire service Reuters that was picked up by other media was, "WHO Warns Against People Mixing And Matching COVID Vaccines." 

That sparked concern among some readers about Canada's vaccination approach, which includes mixing vaccines. 

A day later, Reuters issued a clarification on Twitter.

The wire service also updated the headline on the story to read: "WHO Warns Individuals Against Mixing And Matching COVID Vaccines."

Was WHO talking about Canada?

No. Swaminathan was talking about the lack of evidence supporting the need for an additional dose after someone is fully vaccinated.

She was also emphasizing the urgent need for vaccines to get to low and middle income countries where the majority of people have not even had a first dose to protect them against COVID-19, including the delta variant. 

Is WHO suggesting health agencies shouldn't recommend mixing doses?

No. In fact, the opposite is true. 

"At our Global press conference on COVID 19, Dr. Soumya Swaminathan explained that individuals should not decide for themselves, public health agencies can, based on available data," WHO said in a statement to CBC News on Tuesday. 

Swaminathan also sent out a tweet to clarify her position when the misleading story was shared on Twitter.   

"Context is extremely important," infectious diseases specialist Dr. Isaac Bogoch told CBC News Network Tuesday.

He said WHO officials "were really referring to people who had already received, for example, a full course of a vaccine series and then were, you know, for lack of a better word, choosing their own adventure and trying to get additional doses of a vaccine."

WATCH | Dr. Isaac Bogoch clarifies advice on mixing vaccine doses:

COVID-19: What we know about mixing vaccines

2 years ago
Duration 2:25
Infectious diseases specialist Dr. Isaac Bogoch explains comments from the World Health Organization about COVID-19 vaccines taken out of context and what health experts know about mixing vaccines.

Swaminathan said guidance on mixing and matching vaccines needs to come from public health agencies — which is exactly what is happening in Canada. 

"When public health agencies and advisory committees make recommendations, including on mixed schedules, it is based on data," said Dr. Carolyn Quach-Thanh, pediatric infectious disease specialist and medical microbiologist at Chu Ste. Justine in Montreal. She is also the former chair of NACI.

"We are looking not only at immunogenicity and efficacy, but also need to make sure that the regimen is safe," Quach-Thanh told CBC News on Tuesday.

Is Canada's vaccination approach working?

Yes. Infectious disease experts and epidemiologists widely agree that it is. As more people are vaccinated, COVID-19 cases are declining rapidly across the country, as are hospitalizations and deaths. 

"Completing your vaccine series by getting a second dose is essential to achieve optimal and longer-lasting protection against COVID-19 disease and associated severe outcomes," PHAC said in an emailed statement to CBC News on Tuesday. 

NACI's recommendations on taking a different vaccine as a second dose were issued on June 1, based on evidence and data from other countries — which is the kind of evidence-based approach WHO's chief scientist is advocating. 

Canada has been mixing and matching COVID-19 vaccines for weeks based on emerging research from Spain and the United Kingdom that found combining AstraZeneca with Pfizer shots was both safe and effective at preventing COVID-19.

Because Moderna and Pfizer are both mRNA vaccines, NACI also said that they could be used interchangeably

"Vaccine interchangeability is not a new concept," PHAC said in its statement. 

"Similar vaccines from different manufacturers are used when vaccine supply or public health programs change. Different vaccine products have been used to complete a vaccine series for influenza, hepatitis A and others."

With files from Reuters

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