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A woman receives her COVID-19 vaccine at a clinic at Olympic Stadium in Montreal on March 1, 2021.Paul Chiasson/The Canadian Press

Health Canada says it won’t require new clinical trial data from vaccine makers on booster shots being developed to target new variants of COVID-19.

Instead, the regulator will rely more heavily on lab tests on blood samples, which can show how many antibodies develop following vaccination. Those antibodies are a good indicator of how well the human body will fight off an infection.

The decision should help the regulator authorize the boosters for use in Canada much quicker and is in line with the process used to approve new flu vaccines each year.

At least three variants of the virus that causes COVID-19 are circulating in Canada and are believed to spread more easily and possibly cause more serious illness. Having vaccines adjusted to target those new strains is a critical part of managing the COVID-19 pandemic.

But Health Canada’s chief medical adviser, Dr. Supriya Sharma, said there won’t be corners cut on safety in evaluating new boosters.

Moderna, Pfizer, AstraZeneca or Johnson & Johnson: Which COVID-19 vaccine will I get in Canada?

Canada pre-purchased millions of doses of seven different vaccine types, and Health Canada has approved four so far for the various provincial and territorial rollouts. All the drugs are fully effective in preventing serious illness and death, though some may do more than others to stop any symptomatic illness at all (which is where the efficacy rates cited below come in).

PFIZER-BIONTECH

  • Also known as: Comirnaty
  • Approved on: Dec. 9, 2020
  • Efficacy rate: 95 per cent with both doses in patients 16 and older, and 100 per cent in 12- to 15-year-olds
  • Traits: Must be stored at -70 C, requiring specialized ultracold freezers. It is a new type of mRNA-based vaccine that gives the body a sample of the virus’s DNA to teach immune systems how to fight it. Health Canada has authorized it for use in people as young as 12.

MODERNA

  • Also known as: SpikeVax
  • Approved on: Dec. 23, 2020
  • Efficacy rate: 94 per cent with both doses in patients 18 and older, and 100 per cent in 12- to 17-year-olds
  • Traits: Like Pfizer’s vaccine, this one is mRNA-based, but it can be stored at -20 C. It’s approved for use in Canada for ages 12 and up.

OXFORD-ASTRAZENECA

  • Also known as: Vaxzevria
  • Approved on: Feb. 26, 2021
  • Efficacy rate: 62 per cent two weeks after the second dose
  • Traits: This comes in two versions approved for Canadian use, the kind made in Europe and the same drug made by a different process in India (where it is called Covishield). The National Advisory Committee on Immunization’s latest guidance is that its okay for people 30 and older to get it if they can’t or don’t want to wait for an mRNA vaccine, but to guard against the risk of a rare blood-clotting disorder, all provinces have stopped giving first doses of AstraZeneca.

JOHNSON & JOHNSON

  • Also known as: Janssen
  • Approved on: March 5, 2021
  • Efficacy rate: 66 per cent two weeks after the single dose
  • Traits: Unlike the other vaccines, this one comes in a single injection. NACI says it should be offered to Canadians 30 and older, but Health Canada paused distribution of the drug for now as it investigates inspection concerns at a Maryland facility where the active ingredient was made.

How many vaccine doses do I get?

All vaccines except Johnson & Johnson’s require two doses, though even for double-dose drugs, research suggests the first shots may give fairly strong protection. This has led health agencies to focus on getting first shots to as many people as possible, then delaying boosters by up to four months. To see how many doses your province or territory has administered so far, check our vaccine tracker for the latest numbers.

“They still need to demonstrate that the vaccine that comes out is still safe, effective and high quality,” she said in an interview with The Canadian Press earlier this week.

Canada has authorized three vaccines, from Pfizer-BioNTech, Moderna and Oxford-AstraZeneca, and all are working on various boosters against variants.

The documents supporting Thursday’s decision note that demanding full clinical trials, as was the case for authorizing the original vaccines, would create a serious delay.

“This may also be problematic from a public health perspective since delay in updating a vaccine, where needed, bears the risk that the virus is evolving even further, potentially making a new vaccine version outdated at the time of approval again,” the document says.

Coronaviruses don’t mutate as quickly as flu viruses, but do change as they spread among people and the more they spread, the more they change.

“So a virus is not going to mutate as much when it can’t replicate,” Sharma said.

The existing vaccines have shown reduced effectiveness against the variants of concern, though Sharma cautions the vaccines are still useful even against the variants.

The vaccines Canada has authorized are performing well in countries like the United Kingdom and Israel, where the B.1.1.7 variant is now dominant. That variant is thus far the most common of the three variants of concern in Canada, accounting for more than 90 per cent of about 1,430 variant cases confirmed so far.

Many provinces are now screening all confirmed cases of COVID-19 for the variants of concern, and as many as 10 per cent of all confirmed cases are fully sequenced to look for any mutations to the original virus.

The B.1.351 variant that first arose in South Africa is the most concerning to date in its potential to evade existing vaccines. As of Wednesday, there were 103 confirmed cases of it in Canada.

South Africa stopped using AstraZeneca’s vaccine altogether after lab tests suggested it wouldn’t be very effective against mild illness for B.1.351, which is dominant in that country.

That decision has contributed to growing concerns that AstraZeneca’s vaccine is less desirable but Sharma said the details aren’t that simple.

“Now, if you look at severe disease, or more severe cases, it actually looked like it was still quite protective,” she said.

“But in a country where that is your dominant circulating stream, and in a country where they had potentially had access to another vaccine shortly, they made the decision that maybe they weren’t going to go ahead with that,” she said.

If B.1.351 becomes a dominant strain here, and current vaccines don’t show effectiveness against it, they’ll be pulled, Sharma said.

“We wouldn’t leave a vaccine on the market if we think that it wouldn’t be effective for the overall population.”

Prime Minister Justin Trudeau says extra vaccine shipments could make it possible to vaccinate all willing Canadian adults before September. The United States has an earlier target at the end of May, but Trudeau cautions against using the U.S., with its worse record of infections and deaths, as a guide for what Canada does.

The Canadian Press

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