Everything you need to know about the four COVID-19 vaccines available in Canada

Many Canadians can look forward to a COVID-19 vaccine appointment this month as the number of doses coming into the country increases throughout May.

Although four shots have approval for use by Health Canada, people receiving their first dose this month are likely to receive one of the mRNA shots — Pfizer or Moderna.

The two viral vector vaccines, AstraZeneca and Johnson & Johnson, aren’t being distributed widely by provinces at the moment due to both supply constraints and investigations into rare but severe blood clots.

Pfizer and Moderna are both mRNA vaccines, whereas AstraZeneca and Johnson & Johnson rely on viral vectors to stimulate the immune system.

Curious how each shot elicits protective antibodies? We’ve broken it down:

mRNA vaccines (Pfizer and Moderna)

These vaccines are a relatively new technology. They contain a small piece of the virus’s genetic material that codes for COVID-19’s distinctive spike protein. Wrapped in a lipid nanoparticle envelope, the mRNA, contains the recipe for the virus’s spike protein slips inside the human body’s cells, which read the genetic material and build the viral spike protein.

Immune cells recognize the spike proteins as not belonging, and over the course of a few days to a few weeks, create antibodies to target them. Antibodies are the body’s customized weapons against pathogens and are designed to neutralize the spike protein.

If a vaccinated person comes in contact with the actual COVID-19 virus, the immune system will remember the shape of the spike protein and produce antibodies right away, preventing illness.

Scientists created the mRNA for the vaccine by sequencing COVID-19’s entire genetic sequence and isolating the part that contains the spike protein recipe.

In Canada, Pfizer’s vaccine is approved for use on anyone age 12 and up.

• See also:
  • Here’s the science behind the Pfizer and Moderna COVID-19 vaccines
  • Ontario holds remaining AstraZeneca COVID-19 vaccine for second doses
  • Health Canada authorizes use of Pfizer COVID-19 vaccine for adolescents

Viral Vector vaccines (AstraZeneca and Johnson & Johnson)

This type of vaccine relies on a harmless modified virus to get COVID-19’s genetic material inside human cells. The COVID-19 vaccines use a type of adenovirus that acts as a vehicle to transport COVID-19’s genetic material that codes the spike protein.

Once again, the body’s cells produce COVID-19 spike proteins, which immune cells learn to target and destroy.

One drawback to this type of this vaccine is that some people may already have immunity to the adenovirus that delivers the spike protein genetic material, which may hamper the vaccine’s ability to deliver genetic material.

Why have some provinces stopped giving AstraZeneca?

The AstraZeneca COVID-19 vaccine is associated with rare but severe blood clots involving low platelet counts. Research suggests the risk of developing a clot could be 1 in 100,000, but new cases of clots in Ontario pushed that risk ratio to 1 in 55,000 this month, prompting health officials to stop administering first doses of it.

If someone catches COVID-19, the risk of developing a blood clot or another severe outcome such as death is much higher. Health officials have consistently said choosing the first vaccine available is the best choice because the benefits outweigh the risks.

But as Ontario received more doses of mRNA vaccines, community COVID-19 transmission rates decreased, and reports of AstraZeneca-linked blood clots increased, officials decided to pause and re-evaluate their risk-benefit analysis.

Alberta also stopped giving out AstraZeneca as a first dose, citing supply constraints.

Canada registered to buy 20 million doses of AstraZeneca, but only one million have arrived so far. Many of those shots are now administered, and Ontario says the remaining doses will be used for second-dose appointments.

By contrast, Canada will have received 25 million Pfizer doses by the end of May.

What if I already got a first shot of AstraZeneca?

Health officials say getting the first dose of AstraZeneca was a smart move, especially in areas with high COVID-19 transmission. As the risk of a blood clot is present in the first few weeks after vaccination, medical experts say if 28 days pass with no clot symptoms, recipients are probably in the clear.

Provinces will guide people who received AstraZeneca in the coming weeks on what to do regarding second doses. Research regarding the effectiveness of mix-match dosing is currently underway.

When will the Johnson & Johnson shot be available?

Canada has received a few hundred thousand doses of the single-shot Johnson & Johnson vaccine. However, it will not be available until the country completes an investigation concerning the manufacturing plant.

It’s not known when the Johnson & Johnson shot will be rolled out.

When will I get vaccinated?

Rollout varies by province, but federal officials have said most if not all Canadians will get their first shot by the end of June. All Canadians should be immunized by the end of September.