COVID-19: Second dose of AstraZeneca vaccine no longer recommended in Canada

Pfizer or Moderna now considered a better second dose for someone who had AstraZeneca as their first shot

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British Columbians who chose to get a first dose of AstraZeneca should not get it for their second dose and instead get the Pfizer or Moderna vaccine, a key federal advisory committee said Thursday.

Previously, the National Advisory Committee on Immunization said AstraZeneca recipients could choose whether to get a second dose of the same vaccine, or an mRNA vaccine (Pfizer or Moderna). But in new guidance released Thursday, NACI says Pfizer or Moderna are now “preferred” as the second dose.

The provincial health officer said latest studies show mixing AstraZeneca with an mRNA vaccine could increase immunity to COVID-19.

“It may in some people stimulate a stronger, perhaps more longer-lasting, immune response, so you may get the best of both worlds out of that,” Dr. Bonnie Henry said.

However, a key reason the NACI is moving away from AstraZeneca is because of the risk of blood clotting that is associated with the vaccine and affects one in every 600,000 people who receive that vaccine. AstraZeneca is the vaccine workhorse in the U.K. and Australia, but has been associated with more deaths per capita than the mRNA vaccines.


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In B.C., AstraZeneca was rolled out in March and April during the third wave of the pandemic as a way to immunize high-risk workers and people not yet eligible through the age-based rollout that mostly used Pfizer.

After AstraZeneca-related blood clotting appeared around the world in young people, Henry suspended use of that vaccine for people aged under 30. Around 280,000 British Columbians received a first dose of AstraZeneca vaccine. National figures as of June 5 show that 2.1 million people in Canada had received a first dose of AstraZeneca, but fewer than 16,000 had received it as a second dose.

According to Canada’s COVID-19 vaccine rollout plan, B.C. received 438,000 doses of AstraZeneca – or just under 10 per cent of the total number of doses delivered across the province.

By far, Pfizer is the most available vaccine in the province – with 3,385,590 doses delivered.

Moderna has only made up 17 per cent of deliveries in B.C., with 787,140 doses, however Henry said close to a million doses of that vaccine were expected over the next month.

This is fortuitous, as Pfizer deliveries in July will be significantly less than earlier promised.

“Today we were notified that there’s some upcoming challenges with the deliver of Pfizer vaccines in July, and as a result, the supply that we’ll be receiving in the first two weeks of July is now reduced,” Henry said.

“That is something that happens when we’re in a global pandemic with a global vaccine supply. We know these speed bumps happen, and while disappointing, they’re not unexpected, given the complexity of the global immunization efforts.


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There are no further shipments of AstraZeneca scheduled.

Henry reported 120 new cases over the past day and one death. There are 1,320 active cases of COVID-19 in the community and 131 being treated in hospital, of which 44 are in intensive care.

Twenty per cent of B.C.’s adult population is now fully immunized, while 74.5 per cent of people aged 12 and over have received at least one dose of vaccine.

with files from Canadian Press

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