Ontario stands firm on 12-week interval for AstraZeneca doses — against experts’ advice

In other provinces the gap between vaccine doses is only 8 weeks.

Citing the need for momentum against the growing threat of the coronavirus delta variant, infectious disease experts say they are swayed by the Ontario government’s decision to maintain a 12-week waiting period before people receive the first dose of the AstraZeneca-Oxford vaccine disagree. second dose.

This rule also applies to people who have received their first shot of AstraZeneca and are choosing an mRNA vaccine (Pfizer-BioNtech or Moderna) for their second.

opposite of this, People in Ontario who received the mRNA vaccine Because their first dose can be received only after eight weeks.

Other provinces, including BC, Alberta and Quebec, are now recommending that everyone get their second dose after eight weeks, regardless of whether the first jab is the AstraZeneca or mRNA vaccine.

Speed ​​key to counter Delta variant

Infectious disease experts widely agree that the two doses needed to be fully vaccinated against the coronavirus would provide stronger protection against the delta version of the virus, which has become the dominant strain in the UK and is gaining momentum in Canada.

“There really should be a push to get those second doses faster,” said Dr. Isaac Bogoch, an infectious disease specialist at Toronto General Hospital, who is also a member of Ontario’s COVID-19 Vaccine Delivery Task Force.

“Treat a crisis like a crisis,” Bogoch said. “Even if case numbers are dwindling and hospitals are decompressing and vaccines are rolling out — and frankly that’s all good — you still have a delta variant. You’re still seeing this encroachment on existing variants.” .

“You also have a crystal ball. You can look at the United Kingdom and see what’s really happening there,” he said. “This version will get unvaccinated people and it will get under-vaccinated communities. It is doing this in the UK and it will do the exact same thing with us.”

Bogoch said that getting not only the first dose but also the second dose into the arms as soon as possible after the four-week mark (which experts believe is the minimum interval for effectiveness) is key to preventing this from happening. is.

Decision driven by data, says health ministry

But in an email to Granthshala News on Thursday, Ontario’s health ministry said its decision is driven by scientific data.

“We know that two doses of AstraZeneca at 12-week intervals provide a better immune response than shorter intervals,” the ministry said.

The 12-week hiatus for those receiving the AstraZeneca shot will still apply in the Delta version of “hotspots”, the ministry later confirmed to reporters – even as it is accelerating the second shots for those. starts a program for those who receive mRNA vaccines in those areas.

Dr. Dirk Heuer, Ontario’s chief coroner and another member of the province’s vaccine task force, also defended the 12-week period between doses, noting that the move is “based on available data.”

Not much is known yet, Heuer said, about the optimal time frame between the first dose of AstraZeneca and the second dose of Pfizer-BioEntech or Moderna.

“We will continue to look at everything that is available to us,” he said.

Later on Thursday, Ontario’s associate chief medical officer of health Dr. Barbara Yaffe told reporters that officials would continue to seek more guidance on how to transfer the mixed dose for people who got their first shot of AstraZeneca, but their Want the second shot to be an mRNA vaccine.

No need for a 12-week hiatus, say experts

It’s true that randomized control trials have shown that two doses of AstraZeneca produce the optimal immune response if they are 12 weeks apart, said Dr. Carolyn Kwach-Than, pediatric infectious disease specialist and medical microbiologist at Choo Ste. Justin in Montreal.

But there is no evidence that when people choose the mRNA vaccine instead of AstraZeneca as their second dose, she said.

“You don’t need to wait 12 weeks,” said Kwach-Thanh, who is a former chairman of the National Advisory Committee on Immunization (NACI), but was not speaking on behalf of the NACI.

look | Infectious disease expert says Ontario is making the wrong call on 12-week dose gap:

“I think what comes in handy here is for balance,” she said. “What needs to be discussed at the Ontario level is that when more people get their second dose, they get this benefit over the safety of the first.”

“We all want this delta version to be fully vaccinated before it is very actively circulated in the community.”

Dr Anna Banerjee, an infectious disease specialist at St Michael’s Hospital in Toronto, said that even if one is taking AstraZeneca for both doses, the urgency of protecting people against the delta variant is a more important consideration at this time in the pandemic.

“The risk of exposure is now highest,” Banerjee told Granthshala News Network on Thursday. “There’s no reason to wait 12 weeks.”

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