Spacing COVID-19 vaccine doses 4 months apart a 'risky plan,' says Sask. scientist

·4 min read
Spacing COVID-19 vaccine doses 4 months apart a 'risky plan,' says Sask. scientist
Canada's National Advisory Committee on Immunization released a statement Wednesday recommending 16 weeks between doses when there is limited supply. (Pavel Golovkin/The Associated Press - image credit)
Canada's National Advisory Committee on Immunization released a statement Wednesday recommending 16 weeks between doses when there is limited supply. (Pavel Golovkin/The Associated Press - image credit)

A research fellow at Saskatoon vaccine research facility VIDO-InterVac says stretching doses of the COVID-19 vaccine to four-months is "taking a chance."

"I just want to see the scientific evidence," said Dr. Suresh Tikoo, who is also the director of vaccinology and immunotherapeutics at the University of Saskatchewan.

On Wednesday, Canada's National Advisory Committee on Immunization (NACI) said the time between first and second doses of all three COVID-19 vaccines approved for use in Canada should increase to a maximum of four months apart to boost the number of Canadians being vaccinated.

Tikoo said there is not enough data to support that recommendation and that "no other country or jurisdiction around the world has made such a recommendation."

Earlier this week, B.C. was the first in the world to announce such a long delay between doses.

"It's a risky plan. I would not go for it in the sense that there's no science behind it," Tikoo said.

"The problem is, the data available for the Pfizer-BioNTech vaccine is for about six weeks and AstraZeneca is 12 weeks. But going to 16 weeks or 18 weeks? As a scientist, I would not recommend it myself."

NACI has acknowledged that studies have not yet collected four months of data on vaccine effectiveness after the first dose.

Dr. Suresh Tikoo is a professor and director of vaccinology and immunotherapeutics graduate school and research fellow at VIDO Intervac at the University of Saskatchewan.
Dr. Suresh Tikoo is a professor and director of vaccinology and immunotherapeutics graduate school and research fellow at VIDO Intervac at the University of Saskatchewan.(Mickey Djuric/CBC)

In the U.K., doses are spaced apart by 12 weeks following the emergence of the B117 variant.

"If the virus replicates there are more variants that will arrive. That's one of the main driving forces around this notion, to get the vaccine in as many people as possible, so it lowers the emergence of new variants," Tikoo said.

"They can do eight months, but the problem is there's a risk of seeing antibodies go down after some time."

Spacing doses shows less chance of infection

Steven Lewis, a health policy consultant formerly based in Saskatchewan who now lives in Australia, said he'd go with the U.K. route.

"Get as many arms jabbed with a single dose of whatever vaccine was available and roll the dice that the immunity will hold up," Lewis said in an emailed statement.

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Tikoo and Lewis both said there is a level of gambling when making this decision.

"What are the odds that a single dose of the two-dose vaccines will backfire, leaving people vulnerable after a few weeks and essentially going back to square one with them? We don't know definitively. I strongly suspect it is low," Lewis said.

Recent evidence emerged from the U.K. that a single dose of the AstraZeneca-Oxford or Pfizer-BioNTech vaccines has reduced the risk of hospitalization among older people by 80 per cent.

"When you have results this good, unless there is emerging evidence of a major drop-off in protection after a single dose of a vaccine intended for double doses, I think the case is pretty compelling to go with it wherever there are quite a few cases," Lewis said.

'This becomes a government decision'

Tikoo said if the plan goes wrong, antibodies will neutralize "and there will be more hospitalizations and deaths."

"Companies will never put on their label 'give it four months apart' if they don't have the data," Tikoo said. "They will never give that in writing."

The Moderna COVID-19 vaccine is shown here. Moderna's own trials, and the conditions under which the vaccine was approved by Health Canada, are tied to a four-week interval between doses.
The Moderna COVID-19 vaccine is shown here. Moderna's own trials, and the conditions under which the vaccine was approved by Health Canada, are tied to a four-week interval between doses. (Greg Lovett /Northwest Florida Daily News/The Associated Press)

Patricia Gauthier, head of Moderna's Canadian operations, said the company's own trials and the conditions under which the vaccine was approved by Health Canada are tied to a four-week interval.

"That being said, we're in times of pandemic and we can understand that there are difficult decisions to be made," Gauthier said. "This then becomes a government decision. We stand by the product monograph approved by Health Canada, but governments ... can make their own decisions."

Gauthier said she was not aware of any studies done or led by Moderna on what happens when the interval between the first and second doses is changed from four weeks to four months.