TORONTO -- Canada’s National Advisory Committee on Immunization (NACI) has recommended pausing administration of the AstraZeneca coronavirus vaccine to those under the age of 55 due to fears of recipients getting a rare type of blood clot called vaccine-induced prothrombotic immune thrombocytopenia (VIPIT).

At the time of the initial recommendation, Canada had no reported cases of VIPIT. The first case of a blood clot developing after administration of the vaccine in Canada was announced on Tuesday.

Several provinces, including Alberta, Manitoba, Ontario and Quebec, announced they would follow the guidance, which NACI said stems from investigations of VIPIT cases in Europe.

The European Medical Agency (EMA) said in a statement on April 6 that it had found a "possible link" between the AstraZeneca COVID-19 vaccine and the very rare blood clots. British authorities have recommended the shot not be given to adults under 30 where possible due to the potential risk.

It was believed that VIPIT occurred in about one per million administered vaccines, according to the World Health Organization (WHO), but a report from the Paul Ehrlich Institute in Germany cited potential numbers closer to one in 100,000 doses.

Experts reviewed several dozen VIPIT cases since March that came mainly from Europe and the U.K., where around 25 million people have received the AstraZeneca vaccine. The cases of clotting have been primarily reported in women under the age of 55, with a few cases in men.

Canada’s first case is in a Quebec woman whose age has not yet been revealed. The province said she has received appropriate care, and is recovering.  

European cases of VIPIT have been primarily reported in women under the age of 55, with a few cases in men.

VIPIT refers to a specific type of blood clot that can stem from receipt of the AstraZeneca vaccine and is different from the blood’s regular clotting mechanism or conditions like deep vein thrombosis.

COVID-19 itself has been associated with thrombosis, or blood clots, involving the veins and arteries.

“A blood clot is what you see when the blood coagulates, the platelets stop the bleeding after someone has cut themselves - it's a response of the body to injury,” said clinical researcher and Toronto physician Dr. Iris Gorfinkel in a telephone interview with in March. “It’s really common and it's necessary.”

“But what happens from certain disease states, and that's one of the concerns around the AstraZeneca vaccine, is whether it will cause the blood to clot that's not in a good way, but in a bad way that actually causes…a blood clot to develop in an area and block the blood vessel, and that blood vessel will no longer bring oxygen and nutrients to the area it’s supposed to,” Gorfinkel explained.

VIPIT symptoms usually occur between four and 20 days after vaccination and include persistent and severe headaches, seizures, blurred vision, shortness of breath, chest or abdominal pain and redness in a limb, according to an advisory issued from the Ontario COVID-19 Science Advisory Table.

The advisory states that VIPIT is very rare and it’s not known if certain patients are more likely to get the condition.

At this time the group states they “do not believe that VIPIT is more common in people who have had blood clots before, people with a family history of blood clots, people with low platelet counts or pregnant women because VIPIT does not develop through the same process as usual types of bleeding or clotting problems.”

Despite the extremely rare side effect, the EMA has said the benefits of the AstraZeneca shot outweigh any risks, and the WHO has backed the vaccine. As well, AstraZeneca previously said that its studies have found no higher risk of clots because of its vaccine.

AstraZeneca may not be alone in this risk — Health Canada announced Tuesday that it was closely watching a U.S. investigation into whether the Johnson & Johnson vaccine may be connected to a small number of blood clotting cases. 


While scientists around the world work to understand why these blood clots are happening, a specialized team at McMaster University in Hamilton, Ont. is working to test blood samples from across Canada.

It’s called The Platelet Immunology Lab at McMaster, and the team there is looking for any signs of patients who may develop blood clots linked to the AstraZeneca vaccine.

In a press release on April 13, the lab stated that it has tested 10 blood samples “suspected to be blood clotting issues” linked to AstraZeneca.

“The one positive case was in Quebec,” the release stated, adding that testing can be done within 24 to 48 hours.

More than 700,000 doses of AstraZeneca have been administered in Canada so far. 

A statement from the Public Health Agency of Canada (PHAC) said VIPIT can have serious outcomes, but early diagnosis and treatment can help prevent that.

“Based on current evidence, for those individuals who have already been vaccinated with AstraZeneca for more than 20 days there is no cause for concern,” PHAC said. “For those who have been vaccinated with AstraZeneca less than 20 days, and anyone vaccinated with the AstraZeneca vaccine going forward, you should seek immediate medical attention in the rare event that you develop symptoms starting four days or more after vaccination.”

While many experts stand by AstraZeneca, some doctors are sounding the alarm over the new data.

“These are not ordinary blood clots, they can cause very serious disease in the brain and they can be fatal,” infectious disease specialist Dr. Abdu Sharkawy told CTV News Channel’s Power Play on March 29.

“Even though they are extremely rare, they're very serious and it begs an explanation, it begs an investigation to make sure that if you are going to roll it out potentially over a scale of millions and millions of people, you certainly don't want to put them in harm's way.”

The case fatality of VIPIT is approximately 40 per cent, however, experts say that may decrease with increased awareness.

Dr. Menaka Pai, a specialist in blood clotting disorders and associate professor at McMaster, says it is important to gain a better understanding of who may be at risk of developing these clots as they are hard to treat.

“VIPIT itself is a very aggressive condition so once that clotting starts, unless it's treated, it will not stop,” she explained.

Gorfinkel said it’s very difficult to track down the “why” of rare possible vaccine side effects like VIPIT.

“Was it just a certain population who is susceptible? Could it have been something in the shipment of those vaccines – a temperature deviation? Is it the genetic makeup of those people? Could it be related to something that’s going on in that immediate vicinity that causes a cross-reactivity with a vaccine or something they are exposed to in that area? This is what you’re talking about with rare side effects,” she said.

Gorfinkel also urged people to do research before panicking and said a lot of the answers for NACI’s decision making lies in the math.

“The numbers that we're seeing [of VIPIT] are so far and few between that you will be very hard pressed to find a doctor who's ever seen a case,” she said. “So consider that the World Health Organization estimates this to be one in a million. A regular doctor has maybe 1,500 patients - so how many doctors would it take to get to that million? The answer is way more doctors than I personally even know.”


Gorfinkel said that health agencies may be “worried” about the findings from the Paul Erlich Institute, but said what they “all agree on” is that blood clots are rare.

“It's extremely rare after getting the shot…but the World Health Organization has landed squarely on the [fact that] benefits outweigh the risks, and the European Medicines Agency has said the benefits outweigh the risks, but why NACI is recommending a pause is a little more complicated and it has to do with math,” she said.

Gorfinkel said that “less than 30 per cent of all hospitalizations” and just over four per cent of COVID-19 related deaths in Canada were among those under the age of 55, which shows that is not the cohort typically dying from the disease.

Because health organizations can only give the vaccine at a certain rate due to supply chains and dosage schedules, Gorfinkel said that NACI is asking the question, “‘can we make do with the vaccines that we have for the population who is most risk right now and still get the information we need for the younger people?’”

But Gorfinkel added that the “numbers change completely” if the World Health Organization’s estimate of one in a million VIPIT cases is correct versus the Paul Erlich Institute’s one in 100,000.

“If it's as high as one in one hundred thousand, this is where NACI is drawing the line in the sand, and saying they need to look more closely at it,” Gorfinkel said, adding that because cases of VIPIT are so few and Canada’s population so varied the question becomes: “Is that data necessarily even translatable to what's happening here?…we cannot be sure of that.”

Gorfinkel said some of NACI’s decision making comes to down to the fact that Canada has alternatives to offer instead of the AstraZeneca vaccine.

“NACI’s thoughtfully asking the question, ‘could we not just vaccinate with these others options?’” Gorfinkel said. “This is ultimately why we have Health Canada, why we have NACI and you know, the way it works is Health Canada is a ‘yay or nay,’ is it ‘in or out,’ and NACI does the finer details on it. And generally speaking, the provinces and territories will follow exactly what NACI suggests.”

NACI has recommended the continued use of the AstraZeneca vaccine among people over the age of 55 with informed consent, due to the lower risk of developing of VIPIT in older populations and the increased risk of severe COVID-19 infections among that age group.

For those who have already received the first dose of an AstraZeneca vaccine, European studies involving mixing vaccine doses are currently underway.

Germany's vaccine advisory committee said on April 7 it sees no disadvantages or risks from giving younger recipients of AstraZeneca's COVID-19 vaccine a second dose of an alternative shot. However, Canadian officials have yet to offer guidance on mixing vaccine doses.

Canada has purchased 20 million AstraZeneca doses coming from the U.S. Another two million are being sent from the Serum Institute in India and another 1.9 million from COVAX, a global vaccine sharing network designed to assist mostly middle to low-income countries.


With files from Reuters, CTV's medical specialist Avis Favaro, CTV National News producer Elizabeth St. Philip, writer Ben Cousins, writer Alexandra Mae Jones, and writer and producer Ryan Flanagan