Focus On
Dr. David Williams, Chief Medical Officer of Health, Ontario

Ontario puts use of AstraZeneca vaccine on pause amid increase in serious blood clots

Wednesday, May 12, 2021 @ 2:37 PM | By John Schofield

Last Updated: Wednesday, May 12, 2021 @ 3:32 PM

Ontario is putting use of the AstraZeneca vaccine on hold due to the increasing incidence of rare but potentially life-threatening blood clots.

That brings to three the number of provinces interrupting use of the jab, which is also known as Covishield and was developed jointly by Oxford University and British-Swedish pharmaceutical giant AstraZeneca. On May 12, Nova Scotia said it is pressing the pause button on the vaccine due to lingering safety concerns and more than 1,000 cancelled appointments as Nova Scotians opt for the Pfizer-BioNTech and Moderna vaccines instead. And on May 11, Alberta announced that is has stopped administering first doses of the vaccine for now due to a lack of supply.

 Dr. David Williams, Ontario’s chief medical officer of health

Dr. David Williams, Ontario’s chief medical officer of health

In a May 11 statement, Dr. David Williams, Ontario’s chief medical officer of health, said the decision was made out of an “abundance of caution” because the incidence of the clotting condition, known as vaccine-induced immune thrombotic thrombocytopenia (VITT), has reportedly increased in recent days to 1.7 cases per 100,000 doses administered from 0.9 to 1 case per 100,000 doses.

More than 853,000 Ontarians have already received the AstraZeneca vaccine.

According to news reports, three deaths in Canada have been linked to VITT caused by the AstraZeneca vaccine — an Alberta woman, a woman in Quebec and a person in New Brunswick, whose gender was not revealed. Ontario officials said there were eight cases of VITT in the province as of May 8, with the rate rising from one in 100,000 to one in 60,000.

Williams said health experts across Canada are reviewing the data to decide on the future use of the AstraZeneca vaccine, including for second doses. Depending on the scientific data, the options could include using Pfizer-BioNTech or Moderna vaccine for the second dose.

“Data from the U.K. points to a much-reduced risk of VITT in second doses of AstraZeneca,” said the statement, “and we look forward to providing more guidance in advance of people’s needing to receive their second dose of the AstraZeneca vaccine.”

The growing supply of Pfizer and Moderna doses also played a role in Ontario’s decision to pause administration of the AstraZeneca shot, said Williams, although more than 254,000 doses of the AZ vaccine are expected to arrive in Ontario the week of May 17. The chief medical officer of health said eligible Ontarians who opted to minimize delay and receive an AstraZeneca dose for their initial vaccination did “absolutely the right thing to prevent illness, and to protect their families, loved ones and communities” — especially considering the spread of more infectious COVID-19 variants.

In a May 12 news release and news conference, Deputy Premier and Health Minister Christine Elliott said more than 50 per cent of Ontarians aged 18 and over have received their first dose of a COVID-19 vaccine, and the province is on track to administer first doses to 65 per cent of Ontario residents aged 18 and over by the end of May. She added that the province is working on plans to begin vaccinating children aged 12 and older as early as June.

In another news release dated May 12, the government announced the launch of a rapid testing portal to make it easier for essential businesses to access free rapid testing for COVID-19. Businesses can obtain free rapid-testing kits under the Provincial Antigen Screening Program by first registering at

In the past two weeks, the release stated, the government has received orders for more than 850,000 rapid tests and is delivering them to small- and medium-sized businesses in more than 40 communities across the province. The program is being offered in partnership with the Ontario Chamber of Commerce.

Ontario’s Official Opposition NDP urged the government to continue focusing its vaccination campaign on hot spot areas and not to follow through on plans to return to distribution on only a per capita basis starting the week of May 17.

“Now that we have a steady supply of vaccines, we have a chance to put out the hotspot fires,” NDP Leader Andrea Horwath said in a May 12 news release. “Instead, the Ford government is going to leave them smouldering. It could set the entire province back again.”

Meanwhile, new cases of COVID-19 continued to trend down in the province, with 2,320 reported on May 12. But the number of virus-related deaths remained high at 32. Of those, one person was between 20 and 39 years of age and five were between 40 and 59. To date, a total of 8,374 Ontario residents have died of the illness.

On May 12, the seven-day rolling average of new cases dropped to 2,826, down from 3,432 on May 5.

If you have any information, story ideas or news tips for The Lawyer’s Daily please contact John Schofield at or call 905-415-5891.