Canada’s national vaccine advisers sowed confusion around the AstraZeneca vaccine Monday when they recommended those at a lower risk of COVID-19 wait for a mRNA shot that doesn’t seem to carry a rare chance of a blood clot.
Public health experts responded by doubling down on their own messaging — that all Canadians need to seek out any vaccine available for immediate protection against COVID-19 — and emphasizing that AstraZeneca continues to be recommended by Health Canada against the virus that has overwhelmed Ontario hospitals with sick patients.
Infectious disease experts say the statements from the National Advisory Committee on Immunization have caused frustration when what Canadians need instead is a clear understanding of the risks of AstraZeneca and how to watch for side effects, while recognizing how demonstrably beneficial the vaccine has been to populations worldwide.
“All these vaccines are incredibly effective, all of them improve hospitalization, death, disability and even prevent COVID-19 transmission said Dr. Zain Chagla, an infectious diseases doctor and associate professor at McMaster University, referring to the NACI’s comments.
An uproar ensued on social media among health experts after the NACI said Monday that Canadians who aren’t at a high risk of COVID-19 may wish to wait until they can choose to get a shot of Pfizer or Moderna, mRNA vaccines that have not been shown to have the same risks associated with AstraZeneca.
That messaging reinforced what the NACI said in the past few weeks when the age limit was lowered to 30 for AstraZeneca, that they recommend the shot “if the individual does not wish to wait for an mRNA vaccine and the benefits outweigh the risk.”
Dr. Susy Hota, medical director of infection prevention and control at Toronto’s University Health Network, said what we know about AstraZeneca has not changed, despite the messaging from the NACI.
“In terms of what we understand, the risk of the blood clots are very, very low. It’s considered rare, and with transmission being so rampant in parts of the country … the weighing ends up in favour of the benefits of AstraZeneca,” said Hota, adding the idea of a “preferred” vaccine is problematic.
AstraZeneca is an adenovirus vector vaccine, which works by injecting a modified, harmless virus, known as a “vector,” that enters a cell in the body, and tells it to produce an innocuous piece of COVID-19 that prompts the body to create antibodies against the disease. The shot may cause very rare instances of vaccine-induced thrombotic thrombocytopenia (VITT), which is the development of blood clots along with lower levels of blood platelets, which can make it more difficult for the body to stop bleeding.
Currently in Canada, there are eight confirmed cases of VITT that have been reported, Health Canada told the Star in a statement. There has been one fatality. Over 1.7 million doses of AstraZeneca have been given across the country. It’s the same vaccine Prime Minister Justin Trudeau and Premier Doug Ford have received.
Health Canada is engaged in an ongoing safety review of the vaccine. However, after assessing current data as millions of doses of the vaccine have been given worldwide, the department has concluded the risks are “very rare events” and it continues to recommend Canadians take the vaccine.
Chagla said he was troubled by the NACI’s comments that those who are at higher risk of infection — which in Ontario are low-wage, racialized essential workers who have been sidelined by the vaccine rollout — should take AstraZeneca, while those safe at home should opt for vaccines that don’t have the same side-effect profile.
As Ontario continues to tackle a relentless third wave of COVID-19, Chagla doesn’t recommend skipping AstraZeneca if it’s available.
“The situation in Ontario really favours the risk profile of taking the first vaccine you get, and not end up sick, dying, transmitting, hospitalized,” he said.
But with adenovirus vector vaccines, used by both AstraZeneca and Johnson & Johnson, a single-dose shot that has been approved in Canada but has not yet been distributed, it is important to understand the side effects.
In the U.K., about one in 120,000 people have had a blood clot after receiving the AstraZeneca vaccine. At the end of April, Britain’s medical regulator said they have seen 209 cases of blood clots with low platelet counts, out of about 22 million people who have been vaccinated with AstraZeneca. Forty-one people have died following clotting.
In Canada, the rates are around one in 100,000, but they could be higher once the population is combed to check for the side effect, said Chagla. But even one in 50,000 is still very rare, he said.
Clotting has tended to emerge about four to 22 days after the vaccine is given. It seems to be caused by a hyperimmune reaction to the vaccine, which may have to do with the viral vector itself, he said.
“The body just makes a really, really aggressive immune response, and it creates antibodies which start sticking platelets together, which lead to these clots,” he said. “It’s not a late reaction because it’s at the same point that the body is learning to develop immunity.”
Symptoms of these clots could include an unrelenting headache, changes to vision, numbness or tingling in the face, if the blood clot has formed in the head. If they are occurring in the lungs, a person could experience shortness of breath, and in the legs it’s accompanied by swelling and tenderness, Chagla said.
“The sign of low platelets, which is the other part of the syndrome, is any easy bruising or bleeding or rash on the skin, and those are good reasons to get assessed,” he said, adding emergency rooms are now prepared for this and it’s important to seek medical care right away, even if it’s a false alarm.
The vast majority of cases seem to be blood clots in large vessels in the head, he said.
If you are in the process of weighing your risks with AstraZeneca, Hota said it’s important to look at the risks of what could happen if you are hospitalized with COVID-19, when the chances of getting a blood clot are about 15 to 20 per cent.
A study last month from the University of Oxford found that the risk of cerebral blood clots from COVID-19 is about 10 times higher compared to vaccination.
“The benefits of getting vaccinated quickly outweigh the risks of the blood clots, which are very rare. Every day that you wait, it’s an opportunity lost,” she said.