Blood clot risks: Comparing COVID-19 vaccines with common medicines, travel and smoking

WATCH: Tam discusses process for Canadian health regulators following Johnson & Johnson COVID-19 vaccine reports

There are growing concerns around blood clotting from at least two different COVID-19 vaccines.

On Tuesday, Canada reported its first case of a rare blood clot in a person who had received the AstraZeneca COVID-19 vaccine.

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Meanwhile, the U.S. federal health agencies recommended an immediate “pause” in the use of Johnson & Johnson’s single-dose COVID-19 vaccine after six U.S. recipients developed a rare type of blood clotting, called cerebral venous sinus thrombosis (CVST).

This comes after the European Medicines Agency ruled last week that it found a “possible link” between the AstraZeneca coronavirus vaccine and a rare blood clotting disorder after several dozen cases that came mainly from Europe and the United Kingdom.

While the instances have been extremely rare, the reports have raised fears about the safety of these COVID-19 vaccines, especially for those already hesitant about getting the shots. But experts say there are other more common risks for developing blood clots.

“The risk of the virus is much worse than the risk of the vaccine,” said Gigi Gronvall, senior scholar at the Johns Hopkins Center for Health Security.

Blood clots in vessels form when certain elements in the blood thicken and stick to each other, forming a semi-solid mass. This can happen after an injury or post-surgery.

Blood clotting can occur as a side effect to other common medications, such as birth control and hormone replacement therapy, during pregnancy, from long trips and due to smoking. COVID-19 patients can also develop severe blood clots when suffering from the disease.

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The risks of clotting are higher in these cases than from the COVID-19 vaccines themselves, experts say.

“Blood clots are more common with just day-to-day living than they are with any of the vaccines, including the AstraZeneca and the Johnson & Johnson,” said Linda Dresser, an infectious diseases expert and assistant professor at the University of Toronto.

Ben Chan, an assistant professor of global health at the University of Toronto, said the chances of getting blood clots from the AstraZeneca vaccine are “equivalent to the risk of being hit by a car and dying in Toronto in a given year.”

“Yes, these are risks, we should be aware of them, but we need to put them into perspective compared to the daily risks that we have in our lives around us,” he told Global News in an interview.

“Just about every medication that we take has some potential for side effects, and all those medications have great advantages to us. They help us keep alive.

In a recent analysis, Chan estimated that the delay in vaccination by a few days can expose us to a higher risk of death from COVID-19 than the risk of a blood clot due to the AstraZeneca vaccine.

The U.S. Food and Drug Administration (FDA) estimates that the likelihood of developing a blood clot for birth control users is three to nine women out of 10,000, every year.

Pregnant women are five times more likely to experience a blood clot compared with women who are not pregnant, according to the Centers for Disease Control and Prevention (CDC).

Deep vein thrombosis (DVT), which is a type of blood clot in the deep vein, can also take place during childbirth and up to three months after giving birth.

“Some people have the tendency to get blood clots, so it’s not necessarily a drug, but it’s a combination of the drug and the patient’s background,” said Alexandra Bastiany, an interventional cardiologist at the Thunder Bay Regional Health Sciences Centre in Ontario.

A number of studies have shown that smoking cigarettes increases the risks for blood clots.

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A 2013 systematic review of 32 studies found that so-called ever-smokers (current and former smokers combined) were 17 per cent more likely to develop venous thromboembolism (VTE) – a type of blood clot that starts in the vein – than those who had never smoked.

Smoking directly affects the coagulation properties, so it causes the platelets in the blood to stick to each other,” said Bastiany.

Long trips when you have to sit for an extended period of time can affect blood circulation, particularly in the legs, causing blood clots.

“If you are on a flight that’s over four hours, we know that your risk of a blood clot goes up quite significantly compared to the average of not being on a flight,” said Dresser.

This is why experts recommend standing up and walking during long flights or even wearing compression stockings to prevent clots.

— With files from Global News’ Jackson Proskow 

© 2021 Global News, a division of Corus Entertainment Inc.

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