Citing the need for speed in the face of the growing threat of the coronavirus delta variant, infectious disease specialists say they disagree with the Ontario government’s decision to maintain a 12-week waiting period before people who have received their first dose of the AstraZeneca-Oxford vaccine can get their dose the second.
This rule applies even to people who have taken the first shot of AstraZeneca and are choosing the mRNA vaccine (Pfizer-BioNTech or Moderna) for the second time.
On the other hand, People in Ontario who have received the mRNA vaccine Their first dose can get their second dose just eight weeks later.
Other provinces, including British Columbia, Alberta and Quebec, now recommend that everyone gets their second dose eight weeks later, regardless of whether the first vaccine is AstraZeneca or the mRNA vaccine.
Dynamic speed to counter variable delta
Infectious disease experts broadly agree that the two doses required for a full coronavirus vaccination will provide stronger protection against the delta type of virus, which has become the dominant strain in the UK and is gaining momentum in Canada.
“The motivation really has to be to get those second doses quickly,” said Dr. Isaac Bogosh, an infectious disease specialist at Toronto General Hospital who is also a member of the Ontario COVID-19 Vaccine Distribution Task Force.
“Treat the crisis like it’s a crisis,” Bogoch said. “Even though case numbers are going down and hospitals are decompressing and vaccines are being rolled out — and obviously that’s all good — you still have a delta variable. You still watch for this encroachment of existing variables here.
“You also have a crystal ball,” he said. “You can look at the UK and see exactly what’s going on there.” “This alternative is going to find vulnerable people and it’s going to find vulnerable communities. It’s doing it in the UK and it’s going to do the same here with us.”
Bogoch said getting not only the first doses but also the second doses as soon as possible past the four-week mark (which experts agree is the minimum interval for effectiveness) is vital to prevent this from happening.
The Ministry of Health says the decision is driven by data
But in an email to CBC News on Thursday, the Ontario Department of Health said its decision was driven by scientific data.
“We know that two doses of AstraZeneca every 12 weeks provide a better immune response than one administered over a shorter period of time,” the department said.
The department later confirmed to reporters that the 12-week period for people who received the AstraZeneca shot would still apply in the shifting “hotspots” in Delta – Even when he starts a program to speed up second shots of people who received mRNA vaccines in those regions.
Dr. Dirk Hoyer, Ontario’s chief medical examiner and another member of the province’s vaccine task force, also defended the 12-week interval between doses, noting that the move was based on “available data.”
Huyer said there isn’t much information yet about the optimal time frame between the first dose of AstraZeneca and the second dose of Pfizer-BioNTech or Moderna.
“We will continue to look at whatever is available to us,” he said.
Later Thursday, Dr. Barbara Yaffe, Ontario’s medical director of health, told reporters that officials will continue to seek further guidance on how to space mixed doses for people who get the first shot of AstraZeneca but want the second shot. to have an mRNA vaccine.
Experts say 12-week interval is not required
It’s true that randomized control trials have shown that two doses of AstraZeneca elicit the optimal immune response if 12 weeks apart, said Dr. Carolyn Kwash Tan, a pediatric infectious disease specialist and medical microbiologist at Chu Ste. Justin in Montreal.
She said there is no evidence that this is the case when people choose the mRNA vaccine over AstraZeneca as a second dose.
“You don’t need to wait 12 weeks,” said Quach Thanh, the former chair of the National Immunization Advisory Committee (NACI), but he did not speak for NACI.
Watch | The infectious disease expert says Ontario is making the wrong call about 12-week dose spacing:
“I think what is playing a role here is to strike a balance,” she said. “What needs to be discussed at the level of Ontario is this gain in early protection for more people when they get their second dose.
“What we all want is for us to be fully vaccinated before this delta variant travels very actively in the community.”
Dr. Anna Banerjee, an infectious disease specialist at St Michael’s Hospital in Toronto, said that even if someone were to take AstraZeneca for every dose, the urgency of protecting people from the delta variant is the most important consideration at this point in the pandemic. .
“The risk of exposure is now the highest,” Banerjee told CBC News on Thursday. “There is no reason to wait 12 weeks.”
More to track …
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