CORRECTION: A previous version of this story incorrectly stated that 440,000 people took part in the phase 3 clinical trials of Pfizer’s vaccine. This has now been corrected to state that there were nearly 44,000 participants.
Canadian officials say they will continue to monitor for any additional side effects from Pfizer and BioNTech’s coronavirus vaccine after reports of allergic reactions in the United Kingdom.
Health Canada officially gave the green light to the vaccine from the U.S. pharmaceutical company, deeming it safe for use following a thorough review of the clinical data submitted by Pfizer.
“It’s really important to say that as we monitor the vaccines, adverse event reports will come up,” Dr. Supriya Sharma, chief medical advisor with the regulatory branch of Health Canada, said in a press conference on Wednesday.
“We are always looking for any additional side effects. And that’s why we continue to monitor.
“But it is still a drug, still a vaccine, and there are potential risks even if they are rare.”
In updated guidelines on Wednesday, Britain’s medical regulator, the Medicines and Healthcare products Regulatory Agency (MHRA), advised that people who have a history of significant allergic reactions to a vaccine, medicine or food should not receive the Pfizer vaccine.
Canada’s public health officials said they were working closely with the U.K. government to get additional information, but were not changing their recommendations at the time.
According to Health Canada’s current guidelines, people who have had previous allergic reactions to any of the listed ingredients in the Pfizer vaccine should not get the vaccine.
Pfizer has said people with a history of severe adverse allergic reactions to vaccines or the candidate’s ingredients were excluded from their late-stage trials, which is reflected in the MHRA’s emergency approval protocol.
Sharma said in the clinical trials, out of nearly 44,000 people there were two cases of severe allergic reactions — one from the group that received the vaccine and the other that got the placebo.
“So it wasn’t a significant finding in the trials. However, we know that with all vaccines there’s a risk of allergic reactions.”
It is not uncommon for a vaccine or any drug to result in side effects.
Levon Abrahamyan, a virologist at the University of Montreal, said there was no serious reason for alarm, as it was still unclear what actually triggered the allergic reaction in the two NHS health workers.
“This is normal. There’s nothing alarming” he said.
“Any vaccine…. can cause some allergic reactions for a few people. The issue is what is the percentage.”
The Pfizer vaccine was manufactured using mRNA technology, a new way to make vaccines without using weakened or dead pieces of a virus. The vaccine is comprised of the mRNA, which is the active ingredient, and a series of non-medicinal ingredients.
Sharma said that technically, the allergic reaction could be to any of the components, but “more often than not, with vaccines, it may be an allergy to the non-medicinal ingredients.”
Jean-Paul Soucy, an infectious disease epidemiologist and PhD student at the University of Toronto, told Global News not all adverse reactions are related to the contents of the vaccine itself.
“Some people are just going to have allergic reactions regardless of whether they’re actually getting the vaccine or not. So not every adverse event is actually linked to the vaccine,” he said.
Other side effects reported during clinical trials included discomfort at the injection site, fatigue and headache, but all the reactions were “relatively mild,” Sharma said.
“In total, when we look at the overall population for the clinical trials, the rate of serious adverse events is quite low.
“So I would say to Canadians, we’ve authorized it. If it is their turn to get the vaccine, they absolutely should feel comfortable getting that.
“But we still do need to continue to monitor it, as we would any product.”
Going forward, transparency will be key, Soucy said.
“I am glad the U.K. released this precautionary warning, even if it turns out the allergic reactions were not related to the vaccine itself.
“Building trust between government and the public will be essential to the success of this vaccination campaign.”
In a statement, Pfizer said the regulator’s approval makes Canada the third country in the world to approve the vaccine and that it can start shipping it as soon as it gets the green light that distribution networks are in place.
Canada has a firm order for 20 million doses of the vaccine, enough to inoculate 10 million people, with options to buy up to 56 million more.
For the most part, provincial and territorial health systems will administer the shot, for free, across the country. They will have final say over how to use scarce early supplies in their jurisdictions.
According to preliminary guidance published by the federal government in early November, vulnerable people and those who look after them are high priority, including long-term care residents and some health-care workers.
— With files from Reuters