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Experts say mixing vaccines is OK, after WHO cites limited evidence on the practice

Last Updated Jul 13, 2021 at 8:04 am PDT

Experts are reassuring Canadians who’ve mixed their COVID-19 vaccines that it’s OK, after the World Health Organization (WHO) advised individuals against deciding for themselves to brand shop and in some cases get booster shots on their own.

At the WHO’s Monday coronavirus briefing, chief scientist Dr. Soumya Swaminathan cited little evidence.

“There is a tendency now for people in countries with enough availability of vaccines to voluntarily start thinking about an additional dose. There are people who are thinking about mixing and matching. We receive a lot of queries from people who say they’ve taken one and they’re planning to take another one. So it’s a little bit of a dangerous trend here,” she said. “We are in a data-free, evidence-free zone as far as mix and match.”

Swaminathan later clarified in a tweet that people shouldn’t make those decisions outside of public health regulations, writing: “Individuals should not decide for themselves, public health agencies can, based on available data.”

Swaminathan is urging people to follow their country’s vaccine policies, but headlines that said the WHO was against mix and match vaccines worried some online, prompting experts to try to clear up the confusion and insist what our country is doing is safe.

University of Toronto biomedical engineer professor Dr. Omar Khan told 680 NEWS, while the WHO said little evidence on mixing exists, the body is likely only looking at data from clinical trials, which are done by manufacturers that test their individual vaccine.

“When a manufacturer builds a vaccine and they go through to clinical trials, they don’t ever look at mixing and matching. So all the health and safety data is based on their product only,” said Khan.

“Same thing for the WHO, just like a regulatory body, it looks at all the health and safety data that comes from a clinical trial and these aren’t mixed.”

Khan said while the WHO cannot speak beyond the regulatory data that was submitted to them, Canada’s immunization advisory body is also looking at real world data from several countries.

Early studies have shown mixing vaccines the way Canada is doing, is emerging as a safe way to get people a good level of protection.

Swaminathan noted there has been data on the efficacy of following up a first dose of AstraZeneca with a second dose of Pfizer, which the National Advisory Committee on Immunization (NACI) has recommended.

Based on the similarity of mRNA vaccines, NACI has also said Pfizer and Moderna can be used interchangeably, although it recommends sticking with a single brand when possible.

“No data currently exist on the interchangeability of COVID-19 mRNA vaccines,” NACI advised in its updated guidance. “However, there is no reason to believe that mRNA vaccine series completion with a different authorized mRNA vaccine product will result in any additional safety issues or deficiency in protection.”

“In the end that’s what you want. You want to be able to protect yourself against infection, absolutely protect yourself against severe disease,” added Khan. “Don’t get too worried, getting vaccinated is the right thing.”