Skip to main content
Canada’s most-awarded newsroom for a reason
Enjoy unlimited digital access
$1.99
per week
for 24 weeks
Canada’s most-awarded newsroom for a reason
$1.99
per week
for 24 weeks
// //

A RN draws the vaccine into a syringe at the Saskatoon Tribal Council run vaccination clinic inside SaskTel centre in Saskatoon on April 15.

Kayle Neis/The Canadian Press

Canadian scientists say there isn’t yet enough evidence that healthy adults need a COVID-19 booster shot and that rolling out third vaccine doses too quickly will do more harm than good.

The issue of third doses has become more heated in recent weeks as new research shows that protection against COVID-19 infection starts to slip in some vaccinated individuals over time. In light of the new evidence, Canada’s National Advisory Committee on Immunization now recommends that immunocompromised adults and seniors living in long-term care settings receive a third dose of a COVID-19 vaccine to ensure they have better protection.

Some provinces have expanded third-dose eligibility beyond those groups – for instance, Alberta says anyone 75 or older can receive a third dose, while Manitoba is now offering them to health care workers.

Story continues below advertisement

Canada’s travel restrictions for vaccinated and unvaccinated people, explained

Canada vaccine tracker: How many COVID-19 doses have been administered so far?

But for healthy adults, experts say there’s no need to roll out third doses yet, even as some vaccine makers start to lobby for them. In fact, new data from Toronto’s Institute for Clinical Evaluative Sciences (ICES) show that nearly eight months after being vaccinated, protection against infection and severe outcomes is still very high in non-immunocompromised adults.

The study, which has not yet been published but was presented to a group of physicians and scientists last week, looked at people 16 and older in Ontario who had been vaccinated against COVID-19.

The findings show that, on average, an individual had about 81-per-cent protection against any symptomatic infection of COVID-19 about eight months after their second dose of an mRNA vaccine. Protection against severe outcomes remained well over 90 per cent. When researchers analyzed how well the vaccines protected against the Delta variant, they found similarly strong results.

While the findings also found high levels of protection against infection and severe illness in people who received two doses of AstraZeneca or one dose of AstraZeneca and one mRNA vaccine, those vaccines weren’t offered until March and more time will be needed for follow-up to see how those individuals fare, said study lead Jeff Kwong.

Dr. Kwong, who is a senior scientist at ICES, highlighted the fact that even in seniors 70 and older living in retirement homes, protection against infection and severe disease remained high about eight months after they were vaccinated. Seniors in retirement homes are typically more frail than those living in the community, so that high level of protection is a very positive sign, Dr. Kwong said.

Overall, he said, the vaccines are still holding up well in healthy adults and protection against severe illness is very high, he said.

“The incremental benefit of the boosters is not worth it,” Dr. Kwong said, adding that if and when research shows immunity levels waning in a substantial way, that will be the time to consider an extra shot.

Story continues below advertisement

Until the evidence supporting a third dose is there, it’s a good idea to hold off as long as possible, said Allison McGeer, an infectious-diseases specialist and microbiologist at Toronto’s Mount Sinai Hospital.

While some countries, such as Israel, have started offering booster shots to all who are eligible, Dr. McGeer said there are a few key differences. Israel had widespread access to the vaccine about three months earlier than Canada, and also has higher transmission of COVID-19 than many parts of Canada. So that may mean Canada will also start to use boosters in the coming months, particularly if transmission of the virus spikes and evidence shows immunity levels in vaccinated individuals start to drop substantially.

Dr. McGeer highlighted the fact that giving booster shots too liberally in Canada will further hamper efforts to get first doses to people living in low-income countries. Less than 5 per cent of Africans, for instance, are fully vaccinated.

“If I take my third dose now, I’m taking a dose away from a health care worker in Nigeria – let’s be really clear,” Dr. McGeer said. “If I have a right to a vaccine when vaccinations in Africa are in single digits, even in health care workers, I don’t think that’s something we should expect our governments or our public-health departments to buy into.”

Dr. McGeer said using boosters too early could also complicate efforts to respond to increased transmission of COVID-19 in the months ahead. So instead of prematurely offering third doses when healthy adults still have a strong immune response, it makes more sense to stretch out the protective benefits of the vaccine as long as possible to help keep new waves of the virus at bay, she said.

But some of the current recommendations may have to change if new evidence emerges, Dr. McGeer said. If there are a growing number of outbreaks at long-term care facilities in the weeks after Thanksgiving, it might be necessary to think about third doses for long-term care employees to give an added layer of protection to seniors.

Story continues below advertisement

Some health experts have also been calling for third doses for Indigenous communities. Dr. Kwong said that may be appropriate, given that many Indigenous communities have higher rates of chronic health conditions, which could leave individuals more susceptible to severe COVID-19 infections.

It’s also important to consider safety when thinking about any third doses. For instance, mRNA vaccines have been linked to rare cases of heart inflammation in young men, so any recommendations to roll out boosters in that population need to be considered very carefully, Dr. McGeer said.

Our Morning Update and Evening Update newsletters are written by Globe editors, giving you a concise summary of the day’s most important headlines. Sign up today.

Your Globe

Build your personal news feed

  1. Follow topics and authors relevant to your reading interests.
  2. Check your Following feed daily, and never miss an article. Access your Following feed from your account menu at the top right corner of every page.

Follow the author of this article:

Follow topics related to this article:

View more suggestions in Following Read more about following topics and authors
Report an error Editorial code of conduct
Due to technical reasons, we have temporarily removed commenting from our articles. We hope to have this fixed soon. Thank you for your patience. If you are looking to give feedback on our new site, please send it along to feedback@globeandmail.com. If you want to write a letter to the editor, please forward to letters@globeandmail.com.

Welcome to The Globe and Mail’s comment community. This is a space where subscribers can engage with each other and Globe staff. Non-subscribers can read and sort comments but will not be able to engage with them in any way. Click here to subscribe.

If you would like to write a letter to the editor, please forward it to letters@globeandmail.com. Readers can also interact with The Globe on Facebook and Twitter .

Welcome to The Globe and Mail’s comment community. This is a space where subscribers can engage with each other and Globe staff. Non-subscribers can read and sort comments but will not be able to engage with them in any way. Click here to subscribe.

If you would like to write a letter to the editor, please forward it to letters@globeandmail.com. Readers can also interact with The Globe on Facebook and Twitter .

Welcome to The Globe and Mail’s comment community. This is a space where subscribers can engage with each other and Globe staff.

We aim to create a safe and valuable space for discussion and debate. That means:

  • Treat others as you wish to be treated
  • Criticize ideas, not people
  • Stay on topic
  • Avoid the use of toxic and offensive language
  • Flag bad behaviour

If you do not see your comment posted immediately, it is being reviewed by the moderation team and may appear shortly, generally within an hour.

We aim to have all comments reviewed in a timely manner.

Comments that violate our community guidelines will not be posted.

UPDATED: Read our community guidelines here

Discussion loading ...

To view this site properly, enable cookies in your browser. Read our privacy policy to learn more.
How to enable cookies