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Ontario will proceed with AstraZeneca 2nd doses starting next week

Last Updated May 21, 2021 at 1:39 pm PDT

Ontario’s chief medical officer of health announced Thursday that the province will proceed with second dose administration of the AstraZeneca COVID-19 vaccine next week.

The province says the process will begin with individuals who received their first dose of the vaccine between March 10th and March 19th.

For a limited time, during the week of May 24, individuals who received their first dose can opt for an earlier dose interval of 10 weeks with informed consent. Eligible individuals are being encouraged to contact the pharmacy or health provider where they received their first dose and can start booking an appointment on Monday.

The decision by the Ford government was made in consultation with Dr. Williams and other public health experts.

“Nothing is more important than the health of Ontarians, and for the best protection against COVID-19 it is vital that everyone who received the AstraZeneca vaccine for their first dose receives a second dose of a COVID-19 vaccine,” said Williams.

“We are providing these individuals with a safe option based on the available data and evidence and will continue to work with Health Canada to monitor the quality and efficacy of all COVID-19 vaccines being used in Ontario.”

Ontario is currently sitting on approximately 45,000 doses of AstraZeneca that will expire May 31. According to federal officials, the province is set to receive an additional 250,000 doses this week.

The province says they will provide updated guidance on vaccine mixing in the near future. The update will come in advance of the 12-week interval when most people are needing to receive their second dose of the AstraZeneca vaccine.

Ontario decided they will no longer administer first doses of AstraZeneca on May 11. The decision was made over fears of an increase in a rare blood clotting syndrome reported in some residents.

Blood clotting issues have lingered over the vaccine despite health officials and real-world data showing that the benefits of getting the shot far outweigh the risk of developing the rare side effect.

Nearly one million Ontarians aged 40 and over received the AstraZeneca vaccine as their first dose between March 10 and May 11.


Dr. Theresa Tam said Tuesday she expects Canadians who got AstraZeneca in the first round of vaccinations will be able to choose which vaccine they get for their second dose.

Tam’s comments came hours after a small Spanish study on mixing and matching vaccines reported that giving a Pfizer-BioNTech shot for the second dose after AstraZeneca is safe and produced twice as many antibodies as a second dose of AstraZeneca.

The National Advisory Committee on Immunization (NACI) is still awaiting further data from another mixing-and-matching study underway in the United Kingdom, but Tam said advice on second doses should be ready before most people are due to get their second vaccination.

NACI advised last month that people at low risk of getting COVID-19 should get either Pfizer or Moderna, leading many to wonder if they should risk getting another dose of AstraZeneca.

Tam and Health Minister Patty Hajdu said there will be enough doses of vaccine for AstraZeneca recipients regardless of which kind it is.

“I think everybody’s anxious to make sure people who got the first dose of AstraZeneca do have the ability to get that second dose,” said Tam.


The vaccine rollout continues to ramp up across Ontario.

As of Thursday morning, anyone 12 and older who lives, works, or goes to school in York Region can register for their vaccine.

Halton Region is allowing residents 18 and older to book COVID-19 vaccination appointments a day after the Ford government expanded eligibility provincewide to anyone 18 and older.

Peel Region announced it will open vaccine bookings to youth 12 and up on Thursday. Residents 16 and older were given the green light to begin booking their shots through its local system on Tuesday.

Peel dropped the age eligibility to 16 and older on Tuesday, the same day the province expanded eligibility to all adults provincewide.

Ontario dropped the age eligibility to 40 and up last week, and also expanded to include individuals with health conditions deemed “at risk” and Group Two of people who cannot work from home.

Ontario has said they will be making those aged 12-17 eligible to book their COVID-19 vaccine on May 31 and says there will be specially dedicated youth vaccine clinics during the weeks of June 14 and 21.

The province initially said they hoped to open appointments to all adults next week, but were able to move that up due to an influx of vaccine supply.

Canada is getting an additional 1.4 million shots, which were originally slated to land next week but are now expected to arrive before the upcoming holiday weekend.

The federal government says it now expects around 4.5 million doses to arrive this week from Pfizer and Moderna.

With files from the Canadian Press