OTTAWA -- After receiving his first shot in April, Prime Minister Justin Trudeau says his doctor’s latest advice to him is to take a second shot of the AstraZeneca COVID-19 vaccine, should it be offered to him when the time comes.

“I talked to my doctor just last week, he recommended that I indeed get a second dose of AstraZeneca in the coming weeks or months when it becomes available,” Trudeau said in a response to a question from Conservative MP and health critic Michelle Rempel Garner during question period on Wednesday.

Whether Canadians who have received first doses of the AstraZeneca vaccine will be able to receive a second or have to switch to another COVID-19 vaccine, is one of several questions Canadians have been asking, after some provinces have limited the use of the vaccine this week. The reasoning for the halt is twofold: rising caution over rare blood clotting incidents and a shortage of supply.

In several provinces, the plan is to stop offering first shots of AstraZeneca and to hold on to any outstanding vials to distribute as second shots to those who already have the first. Though in Ontario where Trudeau received his first dose, provincial Health Minister Christine Elliott said Wednesday that a decision has yet to be made about whether AstraZeneca will still be offered as a second shot, leaving open the potential to let doses expire before that call is made.

Conversations are heating up about the prospect of a mixed-dose vaccination regime, and whether it would be possible or even beneficial for those who received a first shot of AstraZeneca. What this would mean is that Canadians who have had a first dose of AstraZeneca, which is a viral vector vaccine, could be offered a mRNA vaccine for their second dose.

Provincial health authorities have said they are awaiting guidance from Health Canada and the National Advisory Committee on Immunization (NACI) about the efficacy of mixing vaccines.

Rempel Garner—who has her first COVID-19 vaccine appointment booked in Alberta for next week— asked Trudeau whether he and others might have to start from scratch and receive two shots of an mRNA vaccine like Pfizer or Moderna, and what his advice is to others who are in a similar position. He urged Canadians to speak with their doctor.

Trudeau said that in his case, his doctor, like all others will “be following the updated guidance that I'm sure will continue to evolve from recommendations by experts on what the right path forward is.”

“I know there are questions being asked around the world about the data that involves mixing and matching doses, there are no recommendations around that yet, but I know scientists are leaning in carefully to see if it may be the right option for many people,” said the prime minister.

Conservative Leader Erin O’Toole, NDP Leader Jagmeet Singh, and many other federal and provincial politicians were among those who received AstraZeneca for their first dose in recent weeks.

In an interview on CTV News Channel’s Power Play on Tuesday, Anand said the government will continue to accept its procured AstraZeneca shipments, but that it’ll be up to the provinces and territories to determine if they still want access to their share of the shipments.

The next shipment of 655,000 doses from Canada’s COVAX contract are expected as soon as next week. To-date approximately 2.3 million doses have been distributed across the country, though Canada has deals to secure approximately 24 million doses of the two-shot vaccine.

Chief Public Health Officer Dr. Theresa Tam’s guidance as of Tuesday was that everyone who received an AstraZeneca vaccine when it was offered to them “did the right thing,” and until the science says otherwise, second shots of the same vaccine will be the focus.

“At the same time, we're following the evolving science… to provide the most up to date advice on whether a mixed-dose schedule is an appropriate way to go, and that would offer a choice essentially, for those who have received AstraZeneca.”

Estimates range in terms of how rare these instances of vaccine-induced immune thrombotic thrombocytopenia, or VIITT, are. Some have pegged the risk of VIITT at between one in every 100,000 to one in every 250,000 people vaccinated with the AstraZeneca vaccine, while Ontario’s recently suggested that the rate in Canada is one in 60,000 doses.

To-date, CTV News is aware of 16 cases of Canadians experiencing VIITT after receiving an AstraZeneca vaccine, and there have been three people who have died after experiencing VIITT following their vaccine.

Health Canada has approved AstraZeneca for use for those 18 and older and that authorization stands. After studying the risks of VIITT, the agency did update the label to note the “safety signal,” but said overall the risks of COVID-19 still outweighed the risks of VIITT.

With files from CTV News’ Sarah Turnbull.