Canada recommends mixing and pairing AstraZeneca, Pfizer and Moderna COVID-19 vaccines

Canada is changing its guidelines on mixing and pairing second doses of COVID-19 vaccines and now advises Canadians to combine AstraZeneca-Oxford, Pfizer-BioNTech or Moderna injections interchangeably in certain situations.

The National Advisory Committee on Immunization (NACI) has updated its guidelines provinces and territories on Tuesday and recommended that a first injection of the AstraZeneca vaccine could be followed by Moderna or Pfizer.

For Canadians who received a first dose of Moderna or Pfizer, NACI recommends that they can now take either of the two injections as a second dose – as they both use similar mRNA technology – if the same first dose is not available or unknown.

The updated NACI guidelines are based on emerging research from Spain and the UK who found mixing and pairing AstraZeneca and Pfizer vaccines to be both safe and effective in preventing COVID-19.

CBC News first reported the details of the recommendation changes on Tuesday morning, based on information from sources with direct knowledge of the decision who spoke on condition of anonymity. Details of the policy change were publicly confirmed by officials from the Public Health Agency of Canada at a press conference on Tuesday afternoon.

Canada’s Chief Public Health Officer, Dr Theresa Tam, said the decision to combine mRNA vaccines interchangeably was “nothing new” and that the same principle had been applied to different types. vaccines in the past – including influenza and hepatitis A vaccines.

“It’s not a new concept, so having a multidose series in terms of vaccines given by manufacturers is something that public health has used over time for many other vaccines,” Tam said. “When vaccine programs and supplies change, it’s not an unusual thing to do.”

The updated NACI recommendations state: “No data currently exists on the interchangeability of COVID-19 mRNA vaccines,” but Tam said there were “ongoing studies” on the effectiveness of the approach that have not yet been published. The decision was made based on the similar composition of the vaccines, both of which target the coronavirus spike protein, she said.

The recommendations will have a major impact on vaccine deployment in Canada, with previous NACI guidelines stating that a vaccine series starting with AstraZeneca should follow the same type of injection and that mRNA vaccines should only be used in the same way. interchangeable only if the same first dose is not available. or unknown.

The updated guidelines follow actions taken by some provinces to combine different vaccines due to supply issues with AstraZeneca and a rare but serious type of blood clot that can occur after the vaccine called vaccine-induced immune thrombotic thrombocytopenia. (VITT), which NACI also cited as the reason for its decision in its guidance.

More than 13 million people have received at least one dose of the Pfizer vaccine in Canada, compared with more than 3.5 million of the Moderna vaccine and more than 2.1 million of the AstraZeneca vaccine as of May 22, according to the latest data available from the federal government.

WATCH | Infectious disease expert says provinces should recommend mRNA vaccines after AstraZeneca

Dr. Isaac Bogoch, member of the Ontario Vaccine Distribution Working Group, explains why some provinces are already recommending an mRNA vaccine as a second dose after the AstraZeneca-Oxford vaccine, and why others will likely follow. 1:14

  • Have a question about the coronavirus or a topical tip for CBC News? E-mail: [email protected] or join us live in the comments now.

Tam said NACI believes the “growing body” of data on AstraZeneca’s follow-up with an mRNA vaccine is sufficient to update its guidelines, and that Canadians should review “all the information they have available. On the risks of the AstraZeneca vaccine.

“The rate of [VITT] after the second dose seems to be lower than after the first dose, but it could increase over time and I think people need to know that kind of information, ”she said. “Currently, 1 in 600,000 people have received this second dose who are having [VITT] – but that could change. ”

Professor Alyson Kelvin, assistant professor at Dalhousie University and a virologist at the Canadian Center for Vaccinology and the Vaccines and Infectious Diseases Organization in Saskatoon, said the guidelines were “appropriate” given the available data.

Kelvin said she believes the Pfizer and Moderna vaccines could be interchanged effectively due to the similarity between clinical trial data and real-world research on the two mRNA-based vaccines.

“I have no problem with mixing and pairing, knowing the components of the vaccine,” she said, adding that there were only slight differences in non-serious side effects with Pfizer having slightly higher reports of mild symptoms. “They’re pretty much tied.”

A registered nurse delivers a Pfizer COVID-19 vaccine to a frontline worker at Vancouver General Hospital in Vancouver, British Columbia, March 4. NACI now recommends that a first injection of the AstraZeneca vaccine can be followed by Pfizer, and that the Moderna and Pfizer shots can be used interchangeably. (Ben Nelms / CBC)

Provinces change their vaccine dose orders

Dr. Zain Chagla, infectious disease specialist at St. Joseph’s Healthcare Hamilton and associate professor at McMaster University, says NACI’s proposed approach to mix and match COVID-19 vaccines is reasonable based on international data available.

“[Pfizer and Moderna] are so interchangeable, I doubt there is a difference between the two, “he said.” Their immune responses should be quite similar.

Manitoba health officials announced Monday that residents who received a first dose of the AstraZeneca vaccine can receive a second dose of Pfizer-BioNTech or Moderna vaccine if they meet provincial eligibility criteria.

WATCH | Manitoba to allow mixing of vaccines:

Manitoba becomes the first province to allow people who received a first dose of AstraZeneca-Oxford COVID-19 vaccine to receive a second dose of Pfizer or Moderna. 2:09

British Columbia provincial health worker Dr Bonnie Henry told a news conference on Monday that British Columbians who have received an initial dose of Moderna or Pfizer will have the option of receiving it. either of the mRNA vaccines as a second injection, with more guidance expected this week on AstraZeneca.

Quebec officials announced in April the province would begin giving a second dose to its most vulnerable residents – even if the second dose did not match the first.

The Public Health Agency of Canada (PHAC) now estimates that the rate of VITT among Canadians who have received the AstraZeneca vaccine is between 1 in 83,000 and 1 in 55,000, with a death rate between 20 and 50 percent, but this is subject to change as more and more data is emerging.

PHAC said in a statement to CBC News on Thursday that there have been 27 confirmed cases of VITT to date in Canada out of two million doses administered, including five deaths among those cases.

Chagla said Canadians who want a second dose of AstraZeneca will have access to it in the coming weeks, but said that once the supply of injections from Pfizer and Moderna becomes more readily available in Canada, it will likely be. deleted.

“The second doses make sense,” he says. “The first few doses are starting to get a little tricky with the arrival of so many vaccines in Canada.”

Registered Nurse Sarah Moslehi prepares a dose of the Pfizer-BioNTech COVID-19 vaccine at a temporary clinic at Woodbine Racecourse and Casino in northwest Toronto on May 5, 2021. (Evan Mitsui / CBC)

Kelvin said future use of the AstraZeneca vaccine must “go hand in hand” with the development of a disease screening mechanism to identify who is most at risk for rare blood clots.

“Until we can do that, we need to at least provide information about your risk in general and discuss the use of other vaccines as a second dose,” she said.

“Having a profile to identify who might be at risk for serious blood clots after the AstraZeneca vaccine would be important moving forward.”

Early research shows vaccine mix to be safe and effective

The Spanish study that informed NACI’s guidelines analyzed 670 volunteers aged 18 to 59 who had already received a first dose of AstraZeneca vaccine, with 450 volunteers who received a dose of Pfizer.

The study found that those who received an initial dose of AstraZeneca vaccine and who received a second injection of Pfizer had a increased IgG antibodies – which are commonly found in the bloodstream and play a key role in creating virus-fighting memory cells – which were 30 to 40 times higher than in a control group that received only a single dose of AstraZeneca.

The results of the Spanish study were announced at a press conference on May 18 and also revealed that the presence of neutralizing antibodies was increased by a factor of seven after a dose of Pfizer – much more than after a second injection. from AstraZeneca.

“If you look at the actual immune response, the study from the Spanish trial showed that if you measure the antibody response in someone who received AstraZeneca and then received the second dose like Pfizer – they mounted a response. really robust immune system, ”Tam said. “So this stimulating response that you want to see is very much present.”

The Spanish study also found that only 1.7% of participants reported serious side effects, which were limited to headaches, muscle pain and general malaise.

The first results of another recent study conducted in the UK, which also informed the guidance of NACI, revealed that mixing different COVID-19 vaccines for second doses could increase a person’s risk for mild or moderate reactions like fatigue, headache or fever – symptoms that could signal a strong immune response.

The results were published on May 12 as correspondence in the medical journal The Lancet and is from the Oxford Vaccine Group Com-Cov vaccine trial, which studies the use of different combinations of COVID-19 vaccines approved for the first and second doses.

Do you have questions about this story? We respond to as many as possible in the comments.

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About Ethel Nester

Ethel Nester

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