As of May 8, Ontario has seen eight cases of VITT.
Quebec says it plans to give those who received a first dose of Moderna a second dose of Pfizer due to supply shortages.
Williams said the province will turn to federal studies to look at whether or not it's safe for those who received an AstraZeneca shot as their first dose to switch to Pfizer or Moderna for their second.
The blood clots are still rare, said Dr. Jessica Hopkins of Public Health Ontario, but the safety signal was tripped and it was prudent to halt the roll-out.
Williams stressed that AstraZeneca recipients made the right decision, based on the advice available at the time, to get that vaccine.
AstraZeneca's controversial COVID-19 vaccine will no longer be administered in Ontario, according to the province's Chief Medical Officer of Health - or rather, the rollout of first doses of AZ will be "paused at this time".
The NCOC, the unified government effort against the pandemic, also said in a statement that out of the 3.5 million SinoVac doses, a consignment of 1 million jabs reach the country on Sunday, while another batch of 1 million doses would arrive between May 13-15.
Over the last few days, there have been increased rates of vaccine-induced thrombotic thrombocytopenia (VITT) from 0.9 per 100,000 doses to 1.7 per 100,000 doses.
Now she worries if her second dose will be a different vaccine brand.
Ontario has given out more than 650,000 doses of the AZ vaccine so far.
New guidelines regarding Covid-19 vaccines have been issued by the Ministry of National Health Services, which restricts the use of the Oxford-AstraZeneca vaccine for women under the age of 40.
Henry said some of the safety data from the United Kingdom study has been reassuring so far and she expects to see more details on the efficacy of combining vaccines in the next couple of weeks.
"For places in Canada in the midst of a third wave, especially for those who don't work from home, the up to 94 percent protection against hospitalization from COVID that one dose of AstraZeneca offers was (and is) valuable", Yammine said on social media.
To a question on joint production of coronavirus vaccines, Smith said the setting up of joint productions takes time and that the U.S. was looking at how it can invest in boosting production.
The demand stems from a row between Brussels and AstraZeneca over a shortfall of tens of millions of vaccine doses the company was meant to have delivered to the European Union since the beginning of the year.
Canada is set to receive approximately 655,000 more AstraZeneca doses in the coming weeks, but they'll be dwarfed by Pfizer shipments coming into the country this month.
The manufacturer recommended timeframe for a second dose of AstraZeneca is four months.