Pressing Pause on First Doses of AstraZeneca


First and foremost, if you received AstraZeneca, we want you to know that you made the right choice to be vaccinated. To go without protection at a time when the COVID-19 virus is circulating widely, would have been significantly more unsafe than the risks associated with the AstraZeneca vaccine. By choosing to receive this vaccine, you protected yourself, your family and your community. Thank you.

“I offer my reassurance to people who have already received the AstraZeneca vaccine,” says Dr. David Colby, Medical Officer of Health, CK Public Health. “You are four times less likely to have a severe reaction to this vaccine than you are to be struck by lightening.”

That said, we know you might have some questions and we hope this provides some answers.


Why did the Government of Ontario choose to “pause” first doses of AstraZeneca?

In short, the rollout was paused out of an abundance of caution. The medical community around the world, including here in Canada/Ontario, are closely monitoring potential side effects associated with all COVID-19 vaccines. When the Government of Ontario noticed that there was an increase in the number of serious blood clotting events after people received their first dose of the AstraZeneca vaccine, they thought it was best to press pause on the rollout. However, AstraZeneca is still being used around the world and in other parts of Canada.

The Pfizer-BioNTech and Moderna vaccines have not been linked to similar adverse side effects and the supply of these vaccines is increasing in Ontario so other options are available.


Why did the government offer AstraZeneca in the first place?

The AstraZeneca vaccine is a very good vaccine that provides significant protection against COVID-19 infections and serious health risks, such as hospitalization and death. In recent weeks, Ontario was experiencing a record number of COVID-19 cases as part of the third wave. It was important that people who were at high risk of suffering serious illness from a COVID-19 infection got vaccinated as soon as possible to develop protection against the virus.

The probability of developing a serious complication, such as blood clots, hospitalization and ICU admissions, from a COVID-19 infection is much higher than the probability of having a serious side effect after receiving the AstraZeneca vaccine.


I already received the AstraZeneca vaccine, what does this mean for me?

Again, you did the right thing by being vaccinated as soon as a vaccine was available to you. Side effects are possible with all medications and vaccines: however, they are rare.

If you received the AstraZeneca vaccine within the last 4 to 28 days and are experiencing new symptoms, such as those listed below, please contact a health care provider for further assessment or go to the emergency department and tell them you have recently received the AstraZeneca vaccine. Symptoms include:

  • a sever headache that does not go away;
  • a seizure;
  • difficulty moving part of your body;
  • new blurry vision or double vision that does not go away;
  • difficulty speaking, shortness of breath;
  • severe chest, back or abdominal pain;
  • unusual bleeding or bruising;
  • new reddish or purplish spots or blood blisters; or
  • new severe swelling, pain or colour change of an arm or a leg.


I received AstraZeneca for my first dose, what happens when it is time for my second dose?

The Province of Ontario is still deciding what to do for second doses. When we know, you will know.

What we do know, is that data out of the UK shows a dramatically reduced risk of serious side effects in second doses of AstraZeneca. Essentially, if you didn’t have a serious side effect from the first dose, you are even less likely to have a serious side effect from the second dose. There is also work being done to determine the effectiveness of a second dose of a different vaccine. So far, results are promising.

For the majority of Ontarians who received a first dose of the AstraZeneca vaccine, it is not yet time to receive your second dose. We know you’re anxious to learn what to do. Once we receive guidance from the Government of Ontario, we will make sure everyone knows what to do and how to book their second dose.


Update (May 21, 2021): The Province of Ontario is proceeding with second dose administration of AstraZeneca for those who received a first dose of AstraZeneca. For a limited time during the week of May 24, individuals who received their first dose of AstraZeneca during the period of March 10, 2021 to March 19, 2021 may opt for an earlier second dose interval of 10 weeks. Individuals are encouraged to contact the pharmacy or primary care provider where they received their first dose to arrange their second dose. For more information, please see the news release from Ontario here.