AstraZeneca COVID-19 vaccine has 'stronger link’ to blood clots, but benefits outweigh the risk to all ages, Health Canada urges

Elisabetta Bianchini
·4 min read

Following the first reported case of a blood clot with low platelets after an individual in Quebec received the the COVISHIELD Serum Institute of India version of the AstraZeneca COVID-19 vaccine, Health Canada still maintains that the vaccine is safe, even for all age groups.

"We know that the risks of getting these side effects from the vaccine are very rare and we know that the risk of getting infected with COVID-19 and potentially experiencing serious health consequences, hospitalization or even death from the disease, are very real," Dr. Supriya Sharma, chief medical adviser with Health Canada said at a press conference on Wednesday. "Health Canada wants to reassure people that the AstraZeneca vaccines continue to be safe and effective at protecting them against COVID-19 and that the benefits of immunization outweigh the risks."

"Get whichever vaccine is available to you, it's that simple. The longer you wait to get vaccinated the longer you’re not protected."

Health Canada conducted a safety review using evidence shared by U.K. and European Union medicines agencies, data from the manufacturer and Canadian experts to evaluate the risks, treatment and possible risk mitigation measures for these rare adverse events linked to the AstraZeneca vaccine. Dr. Sharma shared that the conclusion of this review was that these rare blood clot events are "possibly linked to the use of the vaccine."

"We feel that there is a stronger link between these adverse reactions and the vaccine itself," she said.

Warning label updated, but not with specific groups

Dr. Sharma added that Health Canada has updated the warning label to reflect this finding, informing Canadians about the potential side effects.

"We didn’t find any specific risk factors, such as age or sex, so we are therefore not requiring that the vaccine label be updated to restrict the use of the vaccine at this time," Dr. Sharma said.

The current precautions on the vaccine tell Canadians to seek medical attention if they develop shortness of breath, chest pain, leg swelling, persistent abdominal pain, persistent headaches or blurred vision, skin bruising or pinpoint round spots beyond the site of vaccination, after receiving the vaccine.

The chief medical adviser with Health Canada explained that these blood clots with low platelets can be detected and treatments are available. She added that the advice is that anyone who experiences this reaction with their first dose of the AstraZeneca vaccine, they should not get the second dose.

Currently, the National Advisory Committee on Immunization (NACI) has recommended that the AstraZeneca be used for individual who are age 55 and older. Following the presentation of updated information from Health Canada, NACI is looking at the recommendations to see if they need to be changed.

Comparing risks of the AstraZeneca vaccine

When asked about comparisons of the blood clot risks with the AstraZeneca and things like birth control pills, Dr. Sharma stressed that different types of clots are being seen, but the risk of clots with COVID-19 is much higher than other circumstances.

"If you are a woman between the ages of 15 and 45, your risk of a blood clot is around one in 3,300, if you take a birth control pill that goes to one in about 1,600," Dr. Sharma explained. "If you are pregnant it goes to one in 300,...right after your pregnancy it goes to one in 100.

"If you are in hospital with COVID-19 your risk of having a serious clot is one in five."

She added that one of the hypotheses about what causes these rare blood clots linked to the AstraZeneca vaccine is an activation of the immune system that leads to platelets being "activated," causing clots and the overall platelet count goes down.

"Heparin is a medication that seems to trigger the same type of reaction," Dr. Sharma said. "We still have heparin on the market,...we still use it for prevention, we use it in syringes, for example, to prevent clots, even though there may be alternatives to it."

"For all of the age groups, especially when we're in the situation where the risk of COVID if moderate or high, as it is in many part fo the country, the benefit of the AstraZeneca vaccines far outweigh the risks in all age groups."