Shomporko Online News Desk: Following safety concerns about the AstraZeneca vaccine, Canada, like several other countries, has been mixing and matching COVID-19 vaccines for weeks.
The World Health Organization’s (WHO) chief scientist warned against that method on Monday, calling it “a worrisome trend” for the following dose as well as booster doses, citing a lack of information about the health impact.
During a virtual news conference, Soumya Swaminathan observed, “There is insufficient evidence on mix and match.”
“Maybe it will be a very good approach but at the moment we only have data on the Oxford-AstraZeneca vaccine followed by Pfizer,” she added.
However, her concerns stemmed from individuals deciding to mix vaccines or take additional doses on their own without public health guidance.
In Canada, the National Advisory Committee on Immunization (NACI) has recommended since June that people who received a first dose of the AstraZeneca vaccine should get an mRNA vaccine — Pfizer-BioNTech or Moderna — for their second dose, unless contraindicated.
People who have received the first dose of an mRNA vaccine should be offered the same vaccine for their second dose, NACI said. But mRNA vaccines can be interchangeable if the same product is not readily available for the second dose, it added.
The non-binding recommendations were based on a range of factors from safety concerns to vaccine supply, said Theresa Tam, Canada’s chief public health officer, during a news conference on June 1.
Some Canadian experts say the benefits of mixing doses outweigh the risk and there is enough evidence in favor of the approach.
“There are real-world data in Canada … that suggests that mixing vaccines is quite effective at producing good antibodies against SARS-CoV-2,” said Alberto Martin, a professor of immunology at the University of Toronto.
While some countries in the Middle East have started offering a third booster shot to their residents, Canada is not recommending doses beyond the second one at this point.
Joanne Langley, a pediatric infectious diseases expert at Dalhousie University, said there was no data so far to suggest that a different second dose was harmful.
“There’s some evidence that it could work as well as the same vaccine and in this case, if you got the AstraZeneca first, it may work better to have mRNA (as a second dose),” she told Global News.
In making its recommendation, NACI cited early data from Europe that suggested that mixing doses of COVID-19 vaccines is safe and effective.
Preliminary results from a University of Oxford study published on May 12 found that mixing the Pfizer-BioNTech and AstraZeneca COVID-19 vaccines may increase the frequency of mild to moderate side effects. But these symptoms were short-lived — lasting no longer than a few days — and there were no hospitalizations or other safety concerns.
Meanwhile, a Spanish trial published on May 18 found that when participants who had already gotten an AstraZeneca vaccine were given the Pfizer dose, the presence of neutralizing antibodies increased sevenfold, substantially higher than the doubling impact seen following a second AstraZeneca shot.
Another study in Germany, which has not yet been peer-reviewed, indicated that combining vaccinations was more effective than giving two AstraZeneca injections at triggering an immune response. Overall, after the mixed series, there was a lower incidence of any systemic reaction.