Health officials say their decision was also influenced by the high and reliable supply of Pfizer and Moderna vaccines.
Dr. Theresa Tam, Canada's chief public health officer, says the government will ensure that people can get their second doses of AstraZeneca's COVID-19 vaccine and Health Canada will continue to review studies on mixing vaccines.
Millions of doses of AstraZeneca have been safely administered in Europe, but concerns linger over a rare type of blood clot seen in an extremely small number of recipients.
"So far the Food and Drug Administration of the U.S. has not certified that these vaccines are available for anyone's use; for export or not", he said.
In a detailed document, the health ministry also iterated that the vaccine is not recommended to anyone below the age of 18; to people with a history of severe allergic reactions to any of its components (e.g polysorbate); to patients with active Covid-19; to people who developed clotting disorder with the first dose of AstraZeneca vaccine; and to individuals who have a fever before getting a shot of the vaccination.
The US is looking at joint production of Johnson and Johnson's COVID-19 vaccine in India and ways to help manufacturers like the Serum Institute of India (SII) to boost production, Daniel B Smith, the Charge D'Affaires of the US embassy, said on Tuesday.
"However, over last few days, there have been increased reports of VITT, with a rate of 1.7 per 100,000 doses administered", said Williams of the rare side effect, which has been reported in 12 Canadians to date, three of whom died as a result of the condition.
Chief Medical Officer of Health Dr. David Williams announced the pause during a hastily-called press conference on Tuesday afternoon. More than 236,000 doses arriving in the province this week alone.
Henry said she is closely watching research being done now in the United Kingdom, where about 60 per cent of people were given AstraZeneca for their first shot. "The remaining supply of about 8,400 doses will be used as second doses", said McMillan in an email.
The European Commission, backed by the 27 EU member states, argues that AstraZeneca has breached a contract stipulating it would deliver 300 million vaccine doses to the EU in the first half of this year.
In addition to the raw materials, Smith indicated there was some uncertainty about the USA sending the AstraZeneca vaccines that had been manufactured and not used.
Williams pointed out that if you didn't have a serious reaction to the first shot, you likely would be fine to get your second dose, but they need to confirm that for sure.
According to Health Canada data, around 1.7 million AstraZeneca doses have been administered in Canada as of April 24.