McMaster lab has screened hundreds of samples for rare blood clots linked to AstraZeneca vaccine

Hundreds of samples have passed through a McMaster University lab over in recent weeks, scrutinized by a team of doctors for a rare, blood-clotting syndrome that has been linked to the AstraZeneca-Oxford COVID-19 vaccine.

Ontario has recorded its 1st death from rare blood clots linked to AstraZeneca

Dr. Ishac Nazy is director of the McMaster Platelet Immunology Laboratory, which has screened hundreds of blood samples for vaccine-induced immune thrombotic thrombocytopenia (VITT). (Supplied by McMaster University)

Hundreds of samples have passed through a McMaster University lab over in recent weeks, scrutinized by a team of researchers for a rare, blood-clotting syndrome that has been linked to the AstraZeneca-Oxford COVID-19 vaccine.

The Platelet Immunology Laboratory is the only lab in Canada with the equipment and expertise to test for vaccine-induced immune thrombotic thrombocytopenia (VITT).

That means that the sample from an Ontario man in his 40s, who provincial officials say received his first dose of AstraZeneca near the end of April and died a few weeks later, would have undergone testing there.

Investigation into the man's final cause of death is ongoing, but it has been confirmed that he had VITT when he died, according to Dr. Barbara Yaffe, Ontario's associate chief medical officer of health.

Yaffe said Tuesday that the man's death is the first in the province associated with the rare but serious condition.

Dr. Ishac Nazy is an associate professor of medicine at McMaster and director of the lab at McMaster that specializes in investigation around blood and diseases.

As VITT began to appear staff there pivoted to a new role in a matter of weeks, working to quickly process samples with tests that can be completed in 24 to 48 hours.

"We are working around the clock," said Nazy. "Timely and accurate diagnosis is probably the most important part of resolving this issue."

The doctor noted the suspected cases of VITT outweigh the actual number of cases, but would not say how many samples have come back positive, citing privacy and adding that new samples are coming in every day so numbers are fluid.

Those who received AZ should feel 'very confident'

On Tuesday, Yaffe said 16 cases of serious blood clots known as thrombotic thrombocytopenic syndrome (TTS) have been identified out of the roughly 850,000 doses that have been administered to date.

Thirteen of those cases meet the criteria for VITT.

"The risks associated with this vaccine are rare, but they are real, and I want to extend my deepest and heartfelt sympathies to the family and friends of this individual," said Yaffe.

News of the death may make people who received AstraZeneca vaccine as their first dose feel "uneasy or concerned about their own health and safety," she added.

"I want to take this opportunity to reiterate that those who received the AstraZeneca vaccine should feel very confident in their decision."

Members of the Platelet Immunology Laboratory team are shown during a meeting. (Supplied by McMaster University)

Nazy described the death as "unfortunate," but pointed out the rate of mortality for those with VITT has dropped from 60-70 per cent when it first appeared to roughly 20 per cent, now that health officials are aware of it and can better treat it.

"The fact that we've tested so many in Ontario and this is the first death tells us that we're really good at what we're doing right now from a diagnostic perspective, from a treatment perspective," he said.

'We have to be vigilant'

The incidents of VITT in Canada following a first dose of AstraZeneca are currently at about one in 60,000, said Nazy.

But when it comes to a second shot of the vaccine the risk of clotting is much lower — approximately one tenth or one in about 600,000, he said.

Those who accepted the level of risk associated with the vaccine the first time around should feel comfortable getting a second shot, now that Ontario is offering some residents doses that are set to expire May 31, Nazy said.

In the meantime, the lab doesn't plan to stop testing anytime soon.

"We have to be vigilant about this," said Nazy.

"The risk is not zero, and as long as the risk is not zero we're prepared to continue to do our work to make sure that this is done properly and we catch every single case and treat it."


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