According to these new NACI recommendations, people who have received a first dose of the AstraZeneca vaccine can be offered the same vaccine, if they wish, or else receive the Pfizer-BioNTech or Moderna vaccine, unless contravened. indications.
Also, people who have received a first dose of an mRNA vaccine, i.e. Pfizer or Moderna, should be offered the same vaccine for the second dose.
In the case of mRNA vaccines, either one can be given for the second dose, if the one received in the first dose is not available.
It’s good news that people can choose, said Dr. Theresa Tam, Chief Public Health Officer of Canada, at a press conference Tuesday in Ottawa.
NACI also recommended that the second dose of vaccine be offered as soon as possible.
A nurse administers a Pfizer vaccine to a frontline worker at Vancouver General Hospital.
Photo : Ben Nelms/CBC
NACI says it came to this conclusion taking into account the risk of serious blood clots noted during vaccination with AstraZeneca as well as the possibility of greater temporary side effects when the second dose is not of the same vaccine as the vaccine. first.
Millions of people around the world have received two doses of AstraZeneca and that is great, said Dr Howard Njoo, deputy chief administrator at the Public Health Agency of Canada. Others, who take into account the data on this low risk [lié à l’AstraZeneca], will prefer to turn to this other option provided by this NACI recommendation.
However, interchanging the vaccines, either receiving AstraZeneca first and then Pfizer or Moderna, could result in slightly increased side effects for the recipient, Dr. Theresa Tam explained in substance.
Dr. Tam further explained that when it comes to vaccines, flu or other, it is not new or unusual for different vaccines to be given, depending on vaccination programs and supply.
The ball is in the provinces’ court
The provinces will now have to decide whether to follow NACI’s advice.
In Quebec, Dr. Horacio Arruda, national director of public health, recalled that the province already offered this choice:
it has already been said that people who have received AstraZeneca and do not want to receive an AstraZeneca vaccine as a second dose could switch between.
In Manitoba, health officials announced Monday that residents who received a first dose of AstraZeneca could receive a second dose of the Pfizer or Moderna vaccine, if they meet provincial eligibility criteria.
In British Columbia, Chief Medical Officer of Health Dr. Bonnie Henry said those who received a first dose of Moderna or Pfizer will be able to receive either of the mRNA vaccines as a second dose. Further guidance is expected this week for AstraZeneca.
Decrease in cases
According to the latest federal government data, as of May 22, more than 13 million people had received at least one dose of Pfizer vaccine in Canada, compared to more than 3.5 million for the Moderna vaccine and more than 2.1 million. for the AstraZeneca vaccine.
In Canada, health authorities have identified fewer than 2,700 cases of COVID-19 daily during the last week. This is a decrease of 70% compared to the most acute phase experienced by the country during the third wave.
The number of people with a severe and critical form of the disease has also declined. The number of reported deaths is down 25%; it is 39 per day.
Alyson Kelvin, virologist at the Canadian Center for Vaccinology
Photo: The Canadian Press / Liam Richards
Expert advice across the country
Alyson Kelvin, Assistant Professor at Dalhousie University and Virologist at the Canadian Center for Vaccinology and the Vaccine and Infectious Disease Organization in Saskatoon, said the guidelines were
Ms Kelvin believes that Pfizer and Moderna vaccines can be traded effectively because of the similarity between clinical trial data and research.
I have no concerns about mixing and pairing the two vaccines as I know the components of the vaccine […] They are more or less on an equal footing.
Dr Zain Chagla, infectious disease physician at St Joseph’s Healthcare Hamilton and associate professor at McMaster University, agrees. He believes that the approach proposed by the CCNINational Advisory Committee on Immunization to mix and match COVID-19 vaccines is reasonable, given the available international data.
[Pfizer et Moderna] are so interchangeable that I doubt there is any difference between the two […] Their immune responses should be quite similar.
A logical and necessary recommendation
Interviewed at All morning, André Veillette, immunologist, member of the Montreal Clinical Research Institute and member of the federal working group on COVID-19 vaccines, thinks that
we were going gradually, already, towards what the CCNI has just announced.
In the light [des recherches en Espagne et au Royaume-Uni] and the need to get people vaccinated as quickly as possible with a second dose, the fact that some people do not want to receive AstraZeneca, the fact that we don’t have a lot of this vaccine coming in over the years. next few weeks, I think that’s a logical and necessary recommendation.
The safe and effective vaccine mix, according to early research
The Spanish study behind the recommendations of the CCNINational Advisory Committee on Immunization analyzed data from 670 volunteers aged 18 to 59 who had already received a first dose of AstraZeneca vaccine, as well as 450 volunteers who had received a Pfizer dose.
The study found that those who received a first dose of AstraZeneca vaccine and a second dose of Pfizer had an increase in IgG antibodies – which are commonly found in the blood and play a key role in the creation of memory cells. that fight the virus – which was 30 to 40 times higher than in a control group that received only one dose of AstraZeneca.
Results from the Spanish study, announced on May 18, also found that the presence of neutralizing antibodies was seven times higher after one dose of Pfizer – significantly more than after a second dose of AstraZeneca.
The study also found that only 1.7% of participants reported serious side effects, limited to headaches, muscle pain, and general malaise.
The results of another recent study carried out in the United Kingdom, which also served as the basis for the recommendations of the CCNINational Advisory Committee on Immunization, have shown that mixing different COVID-19 vaccines for second doses may increase the risk of mild or moderate reactions such as fatigue, headache or fever – symptoms that could signal a strong immune response.
The results were published on May 12 as a correspondence in the medical journal The Lancet and come 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 dose.