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."

"This decision was made out of an abundance of caution due to an observed increase in the rare blood clotting condition, known as vaccine-induced immune thrombotic thrombocytopenia (VITT), linked to the AstraZeneca vaccine," said Dr. David Williams in a statement announcing the news on Tuesday.

"In collaboration with health experts at Public Health Ontario, the Science Advisory Table and our federal, provincial and territorial partners, we are reviewing the data to consider options for the use of the AstraZeneca vaccine for second doses and more broadly moving forward."

Ontario is pausing 1st doses of AstraZenca vaccine today as per Dr. David Williams, the Chief Medical Officer of Health,

He cites:
1. Risk of thrombosis
2. Greater supply of mRNA vaccines

Those with 1st dose of AZ will either get a 2nd dose of AZ or perhaps an mRNA vaccine.

— Isaac Bogoch (@BogochIsaac) May 11, 2021

According to the provincial government, more than 850,000 doses of the AstraZeneca/COVISHIELD vaccine had been administered in Ontario as of May 8 with a VITT rate of 0.9-1 per 100,000 doses.

"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.

People over 40 have been rushing out to pharmacies for the AZ vaccine since Ontario opened it up to their age group on April 20, which may be why #GenXZeneca is trending on Twitter following Williams' announcement.

It is not yet clear if Ontario will be reccomending a second dose of AstraZeneca for those already injected, but the government did note in a release this afternoon that data from the U.K. "points to a much-reduced risk of VITT in second doses" of the vaccine.

Finally, those who got AZ - don’t panic/feel remorse. You received a very efficacious vaccine that will protect against severe illness

Remember risk is low, but be familiar w symptoms, seek immediate care. Print & take this, request interpreter at hospital for language barriers. pic.twitter.com/syT8lhypmP

— Sabina Vohra-Miller (@SabiVM) May 11, 2021

"We look forward to providing more guidance in advance of people needing to receive their second dose of the AstraZeneca vaccine," said Williams, who noted that the decision to pause AZ was made not only due to VITT, but as the result of increasing supplies of other vaccines (specifically those by Pfizer and Moderna).

Officials also maintain that people who already got the AstraZeneca vaccine "did absolutely the right thing" to protect themselves and others from what's turned out to be a deadly third wave of COVID-19.

"The health and safety of Ontarians remains our top priority. Ontarians are encouraged to get vaccinated as soon as they are eligible," said Williams." The right thing to do to protect yourself and those around you is to get vaccinated with the vaccine you were eligible to receive.”