The Ontario government will pause administering first doses of the AstraZeneca vaccine for now amid increased reports of blood clotting.

Chief Medical Officer of Health Dr. David Williams announced the pause during a hastily-called press conference on Tuesday afternoon.

He said that that the decision is being made in response to new data that suggests the risk of vaccine-induced thrombotic thrombocytopenia (VITT) may be higher than initially thought – about one in 60,000 people rather than one in 125,000.

“It is not that the risk for individuals has gone up extensively at this time but because it is sometimes severe we want to be cautious and say ‘Let's pause it’ while we look at the data and information,” he said. “We maintain that those who received their first dose with the AstraZeneca vaccine did absolutely the right thing to prevent illness, and to protect their families, loved ones, and communities.”

There have been eight cases of vaccine-induced blood clotting reported in Ontario so far and while the condition remains extremely rare, it can be fatal.

Williams said that with supply of other vaccines, specifically Pfizer, ramping up considerably the province found itself in a position in which it could suspend the use of AstraZeneca for now “out of an abundance of caution.”

He also said that the declining case numbers in Ontario were a factor in the decision, as it could mean that the risk of ending up in hospital from a vaccine-induced blood clot will eventually exceed the risk of being hospitalized due to COVID-19.

“When you look at risk on a population level what we're really looking at is you know overall does this safety signal give us enough concern that we preferentially choose other products. At this point in time, and given that we're seeing the overall case numbers of COVID going down, and an increase in the safety signal at a population level, it makes sense to pause AstraZeneca because the risk of severe outcomes with VITT shouldn’t be underestimated,” Chief Health Protection and Emergency Preparedness Officer Dr. Jessica Hopkins said during the press conference.

The decision to pause the use of AstraZeneca in Ontario comes with the province still in possession of about 50,000 doses, though there are not currently any future shipments scheduled due to supply issues.

The remaining supply will be reserved for second doses, as research out of the United Kingdom has suggested that the risk of blood clotting goes down to one in a million after the first dose.

Those who got AstraZeneca when they could did the right thing: experts

Speaking with CP24 Tuesday night, a number of experts said that those who got AstraZeneca when they could should not feel like they made the wrong call.

“I think it's still important to remember that if you've gotten the shot and you got it during a period where community transmission was high, you've probably saved your life if not countless other lives,” infectious disease expert Dr. Abdu Sharkawy told CP24. “There's plenty of ICUs that were full of young people who had the option of taking the AstraZeneca vaccine and didn't take it.”

Neuroscientist Samantha Yammine agreed.

“When many of you who may be watching made the decision to get your AstraZeneca vaccine, we were in the midst of a third wave. We were breaking records in Ontario,” she said during a panel interview on CP24 Tonight. “You made a good decision to get that protection as soon as you could. There were hundreds of deaths this past month and because of this vaccine, because people took the first vaccine including AstraZeneca, there are so many lives that were saved.”

The scientific director of Ontario's COVID-19 Science Advisory Table, Dr. Peter Juni, said that he and his wife decided she would to try get an AstraZeneca shot several weeks ago when schools were still open, but were unable to.

Given the new data around the vaccines and the fact that his family is no longer as exposed, he said they would not try to get an AstraZeneca shot if they could today.

“Now our children are not in school anymore, we are completely in social isolation actually my family and myself, and in the situation we are in today, I would advise her against getting it and to wait for the Pfizer or Moderna vaccine,” Juni said. “So things change depending on your exposition and on our understanding (of) what goes on.”

Bioethicist: message confusing

The new direction around the AstraZeneca vaccine in Ontario is just the latest twist in what has been a very windy road for the narrative surrounding the shot.

Originally the vaccine was only available to younger people, then it was only available to older people and then most recently Canada's National Advisory Committee On Immunizations (NACI) said it should be available to anyone over 30 who wants to get it, but only if they don't want to wait for an mRNA vaccine.

Bioethicist Kerry Bowman told CP24 that the messaging has been “absolute confusion.”

“I appreciate the nuanced arguments that everybody's putting forward but that's asking an awful lot of a lot of people that are looking for some very clear direction,” he said.

He pointed out that ever-changing advice creates confusion and mistrust on the part of the public and said that potential supply issues with other vaccines could eventually force the government to backtrack on AstraZeneca once again.

“We've really wobbled back and forth and we're gonna pay quite a price for it on this front of vaccine hesitancy,” he said.

However Sharkawy said that while clear communication is a challenge, the government is right to pivot when the situation changes.

“It’s not mixed messaging, I think it is responsible adaptation to what's going on within your community and what your risk exposure is and it's gonna take some time for people to wrap their heads around that because the messaging hasn't been perfect, but we have to start somewhere,” he said.