Ontario is dedicating its remaining AstraZeneca COVID-19 vaccine supply to administering second doses after pausing first doses of the vaccine due to blood clot concerns.
During a technical briefing Wednesday, officials said the risk of a rare but dangerous blood clot following vaccination is much lower from the second dose compared to the first.
“Data out of the UK shows a dramatically reduced risk of the adverse reaction called VITT in second doses of AstraZeneca,” Health Minister Christine Elliott said at a news conference. “We are also seeing promising results from administering a second dose of a different vaccine.”
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Ontario stopped giving first doses of AstraZeneca on Tuesday after a several recent reports of blood clots following immunization increased the rate above the expected risk of approximately 1 clot per 100,000 doses.
The risk figure in Ontario now looks closer to one clot per 55,000 doses.
“Those of you who received the first dose of AstraZeneca did the right thing to protect yourselves, your loved ones, and your communities,” Elliott said, adding the decision to pause first doses is an “abundance of caution.”
Ontario has about 50,000 AstraZeneca doses remaining in pharmacy and primary care distribution channels. Those shots have expiration dates ranging from late may to late June.
Officials say those doses, plus another 254,000 coming the week of May 17, will be allocated as second doses for people who already received their first shot of AstraZeneca.
Pharmacies began administering AstraZeneca vaccine in March, meaning the earliest second dose appointments should happen in June.
Health officials haven’t said yet whether people who received AstraZeneca as a first dose will have a choice of vaccine for their second dose.
The province is waiting on research from the UK that should indicate whether mixing and matching vaccines is effective.
Guidance from the province is still hazy on the best course of action for people who received a first shot of AstraZeneca, but officials said further advice will be coming soon.
Half of Ontarians have now received their first vaccine dose, and vaccines are reaching the hardest-hit populations after the province focused on hotspots during the third wave.
Children age 12 to 17 should also become eligible for a vaccine in June.