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A patient receives a COVID-19 vaccine at a clinic, as efforts continue to help slow the spread of the coronavirus in Ottawa, Ontario, on March 30, 2021. The 12-week interval for AstraZeneca recipients, which is longer than in other provinces, has prompted frustration.

Blair Gable/Reuters

Joee Wong was one of the first people in his social circle to receive a COVID-19 vaccine in April. But the Toronto resident now expects some of his friends and colleagues, who received their first doses several weeks after him, will likely get fully vaccinated before he does.

The reason? He received an AstraZeneca vaccine.

The Ontario government announced last week that individuals who received a first dose of the AstraZeneca vaccine could choose the same vaccine or another for their second dose, and that these second doses would be available 12 weeks after their first. Meanwhile, the interval between doses for those who received a first dose of the Pfizer or Moderna vaccines is at least 28 days.

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Ontario to speed up second doses in regions with Delta variant; AstraZeneca interval stays at 12 weeks

The 12-week interval for AstraZeneca recipients, which is longer than in other provinces, has prompted frustration. Some are now calling on Ontario to reduce the wait time and deliver second doses as quickly as possible, especially in light of the spread of a highly infectious Delta variant.

According to the Ministry of Health, the 12-week interval for AstraZeneca recipients is to ensure an optimal immune response.

“Given we know that two doses of AstraZeneca at a 12-week interval provides a better immune response than over a shorter interval, Ontario currently recommends the same interval for mixed doses in [an] effort to get the best immune response possible for all Ontarians,” ministry spokesperson Bill Campbell said in an e-mail.

Yet to receive better protection against the Delta variant, which is now rapidly spreading in the country, experts say two doses are needed. According to a British study, the effectiveness of the AstraZeneca vaccine against the Delta variant is about 30 per cent after the first dose, compared with 60 per cent after the second. While Caroline Quach-Thanh, the departing chairperson of the National Advisory Committee on Immunization, did not take a side, she said it “is a real question” whether it’s better to wait at least 12 weeks or to get second doses in arms as quickly as possible.

Which COVID-19 ‘variants of concern’ are in Canada?

Coronavirus tracker: How many COVID-19 cases are there in Canada and worldwide? The latest maps and charts

Not all provinces are requiring a 12-week wait. In B.C. and Alberta, for example, those who received a first dose of the AstraZeneca vaccine can book a second dose after eight weeks.

In April when he became eligible to receive his initial dose of the AstraZeneca vaccine, Mr. Wong said he was willing to get whatever vaccine was available to him first. But now, he said, his biggest concern is that with new variants emerging, a single dose may not provide sufficient protection. And as someone who lives in a multi-generational home and takes care of older adults, he said he wants to make sure he doesn’t fall ill. His second dose is scheduled for July 21.

A 12-week interval is ideal “when we’re not we’re not in the middle of a pandemic and we have the luxury to wait for a maximum optimal immune response,” said pharmacologist Sabina Vohra-Miller, founder of website Unambiguous Science and co-author of a new guide for people who received a first dose of the AstraZeneca vaccine. But given the current situation with the spreading Delta variant, she said it’s more advantageous to administer second doses quickly.

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Tara Kiran, a family doctor at St. Michael’s Hospital and associate professor at the University of Toronto, said the decision to receive a first dose of the AstraZeneca vaccine has already caused a lot of stress and anxiety among recipients, amid concerns over the risk of blood clots. She suggested the guidance around a 12-week interval needn’t be so tight.

“I feel like we kind of owe it to people who got AstraZeneca not to make life even more complicated than it already is for them,” Dr. Kiran said.

She added that while the early decision to delay second doses in Canada was to ensure as many people as possible could get their first, those now choosing the AstraZeneca vaccine for their second dose won’t affect the supply for everyone else.

With files from Ivan Semeniuk

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