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Ontario says delaying COVID-19 vaccine second doses will allow it to rapidly accelerate rollout

The National Advisory Committee on Immunizations has approved delaying second doses of the COVID-19 vaccine up to four months
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A vial of the PFfizer-BioNtech COVID-19 vaccine (Photo courtesy of Communications Nova Scotia)

Canada's National Advisory Committee on Immunization (NACI) is giving the green light for provinces to delay second doses of the COVID-19 vaccine up to four months.

"Based on emerging evidence of the protection provided by the first dose of a two dose series for COVID-19 vaccines currently authorized in Canada, NACI recommends that, in the context of limited COVID-19 vaccine supply, jurisdictions should maximize the number of individuals benefiting from the first dose of vaccine by extending the second dose of COVID-19 vaccine up to four months after the first," reads the updated guidelines.

The change comes just a couple of days after health officials in British Columbia announced that province would be doing exactly that.

"The important thing that we've learned is that these vaccines work, they give a very high level of protection and that protection lasts for many months," said B.C. Medical Officer of Health Dr. Bonnie Henry.

"Extending this second dose provides very high, real world protection to more people sooner," she said.

Here in Ontario, our province has been asking NACI to update its recommendations but said it would wait for the committee to weigh in before following in B.C.'s footsteps.

"We welcome the updated direction from NACI that the interval between the first and second doses of the Pfizer and Moderna vaccines can be safely extended to four months while maintaining a strong and sustained level of protection from COVID-19," said Alexandra Hilkene, a spokesperson for Ontario Deputy Premier and Minister of Health Christing Elliott in a statement. "This will allow Ontario to rapidly accelerate its vaccine rollout and get as many vaccines into arms as quickly as possible and, in doing so, provide more protection to more people."

"With today’s guidance in hand, and as we receive final details from the federal government on AstraZeneca allocations, we are updating the province’s vaccine rollout and look forward to sharing more details on Phase 2."

But the move isn't without risk.

"I would err on the side of being conservative," said Stephanie DeWitte-Orr, an associate professor in health sciences and biology at Wilfrid Laurier University. "I would want to follow the known trial as closely as possible because we know what the results are going to be."

Both the Pfizer and Moderna vaccines represent relatively new vaccine technology being the first messenger RNA (MRNA) vaccines approved for human use in Canada though the technology has been in development for years, already tested on other viruses like Middle East Respiratory Syndrome, or MERS.

"So kind of going rogue with dosage, as a scientist, kind of makes me a little nervous," said DeWitte-Orr.

"My concern is, if you spread the window too far, than you'll have a whole population of people with reduced protection, and it's possible - now we don't know if it actually would happen but it's possible in that situation - if the virus infects those individuals, it'll force that virus to mutate in order to replicate in these partially protected individuals and that could produce escape variants," she said.

Suggesting it's possible pushing the second dose of the vaccine too long could help breed a new variant able to escape the vaccine.

That being said, aside from that possibility, DeWitte-Orr says the decision mostly boils down to vaccine efficacy.

"Scientifically speaking, it's not like if you get two doses too far apart you're going to be sick, it's not something that will make you sick, it's just you might not have that really beautiful 95 per cent protection that you would have if you had the doses closer together."


Casey Taylor

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