TORONTO -- Canada’s National Advisory Committee on Immunization (NACI) is changing its guidelines to allow for mixing and matching COVID-19 vaccines, CTV News has learned.
NACI will update its guidance to the provinces and territories on Tuesday, recommending that a first dose of the AstraZeneca-Oxford vaccine can safely be combined with a second dose of the Pfizer-BioNTech or Moderna shots in certain situations.
The new guidance will also advise that the Pfizer and Moderna vaccines can be mixed for first and second doses as the mRNA technology is similar, sources say.
Federal health officials are expected to announce the new recommendations at a press conference at noon ET.
Current NACI guidelines advise that the vaccination series should be completed with the same COVID-19 vaccine product, meaning those who received AstraZeneca should follow up with the same shot.
The current guidance also says that mRNA vaccines should only be used interchangeably if the same first dose is "temporarily unavailable or inaccessible."
There are currently four vaccines authorized for emergency use in Canada. However, several provinces have suspended the use of the AstraZeneca COVID-19 vaccine for first doses over concerns about the risk of developing rare blood clots.
The update to the guidelines follows moves by some provinces to combine different shots due to issues with the AstraZeneca shot. Manitoba health officials announced on Monday that people who received AstraZeneca as their first dose can get a second dose of either Pfizer or Moderna if they meet provincial eligibility.
It is unclear how soon other provincial health authorities will be able to adjust their vaccine rollouts to take into account NACI's revision for mixing and matching vaccine doses.
Sources say the updated guidance from NACI is based on preliminary study results from Spain and the United Kingdom that found mixing and matching AstraZeneca and Pfizer vaccines was ultimately safe.
Both studies have also found that mixing the two vaccines was effective at preventing COVID-19, and may actually promote the immune system to produce more antibodies.
However, the studies noted that mixing vaccines resulted in more frequent side-effects within 48 hours of receiving the second dose, including fever and fatigue, when compared to "non-mixed" schedules.
Canadian researchers announced earlier this month that they are looking at the effect of using different COVID-19 vaccine doses in Canadian adults to determine if the mix-and-match approach yields a strong immune response and how long that response lasts.
The study involves 1,300 adult participants and will be conducted in conjunction with the COVID-19 Immunity Task Force, Vaccine Surveillance Reference Group, Canadian Immunization Research Network and Dalhousie University.
Canada's Chief Public Health Officer Dr. Theresa Tam said on May 12 she believed Canada would be mixing vaccine doses by the summer. She noted in a press release that data from the new Canadian study will further aid health officials in the fight against COVID-19.
"In addition to international data, this Canadian study will help inform Canada's public health recommendations on the potential to use different combinations of vaccines for the first and second dose, as well as different dosing intervals," Tam said.
As of May 22, more than 13 million Canadians have received at least one dose of the Pfizer COVID-19 vaccine while 3.5 million have received Moderna and over 1.6 million have gotten AstraZeneca, according to data from the federal government.
With files from CTV News' Michel Boyer
Coronavirus: NACI to recommend mixing AZ, Pfizer, Moderna vaccines - CTV News
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