As COVID-19 vaccinations ramp up across the country, a new study in Canada will now look at the safety and effectiveness of mixing and matching different types of shots.
Some 1,300 adult participants are expected to be enrolled in the clinical trials in Nova Scotia, Quebec, Ontario, Manitoba, Alberta and British Columbia, investigating the effects of using two different COVID-19 vaccines for the first and second dose.
The study was launched on Thursday and is being conducted by the COVID-19 Immunity Task Force (CITF), the Vaccine Surveillance Reference Group (VSRG), Canadian Immunization Research Network (CIRN) and Dalhousie University.
“As questions of vaccine interchangeability arise and alternative dosing intervals are being used in public health programs, our objective is to determine: what are the effects of different dosing intervals of the vaccines on immunity and safety?” said Joanne Langley, co-principal investigator of the project and a professor at Dalhousie University, in a statement.
“We also want to know what the immune response is if two doses of different COVID-19 vaccine products are used, and how long these responses last.”
Canada has approved four COVID-19 vaccines — Pfizer-BioNtech, Moderna, AstraZeneca and Johnson & Johnson — all of which will be included in the nationwide trials.
Last week, some provinces stopped administering the use of the AstraZeneca vaccine as a first dose because of safety and supply concerns, leaving recipients awaiting their second shot in limbo.
“I don’t know what will be recommended and I don’t know what my choices are going to be,” said Kerry Bowman, a bioethicist at the University of Toronto, who received his first dose of AstraZeneca in the middle of March, in a previous interview with Global News.
Early data from studies in Europe suggests 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 study released Tuesday showed that the presence of neutralizing antibodies rose sevenfold after people who already received a first shot of AstraZeneca vaccine were given the Pfizer dose, significantly more than the doubling effect observed after a second AstraZeneca shot.
So far, there is no official guidance in Canada about mixing vaccine doses.
“The National Advisory Committee on Immunization (NACI) will be looking at all of the data and provide a recommendation to the provinces,” said Theresa Tam, Canada’s chief public health officer, during a news conference on Tuesday.
“It is likely that people in Canada who have received one dose of AstraZeneca will have a choice for the second dose,” she added.
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