AstraZeneca blood clot risk is real — so is it worth taking?
RISK OF BLOOD CLOTS FROM VACCINE SMALL BUT REAL — BUT IS IT BETTER TO RISK CATCHING COVID?
The 49-year-old perfectly healthy nurse received her first dose of the AstraZeneca COVID vaccine in mid-February. Eleven days later she was dead, a victim of a rare blood-clotting disorder that has regrettably popularized a new pandemic acronym — VIPIT — one that threatens to rattle confidence in vaccines, the only ultimate path out of COVID-19.
On Monday, weeks after a team of German scientists first described the death of the Austrian nurse, and the startling similar cases of others who'd been injected with the Oxford-AstraZeneca vaccine, Canada's provinces temporarily halted use of the shots in people under 55.
The provinces acted on advice from Ottawa's expert panel of vaccine advisers, which decided it prudent to temporarily suspend the vaccines in the under55s due to “substantial uncertainty” about the benefits, given the potential risk of the rare clotting disorder.
But even then, it's not clear how much of a risk: One in a million doses? One in 100,000? The number seems to change based on the estimate of the day.
Josh Greenberg, a professor at Carleton University and expert on health risk communication, said Canadians should take comfort knowing that the regulatory and safety review process appears to be working: A safety signal was detected, and regulators responded. Health Canada has now asked AstraZeneca for a detailed assessment of the benefits and risks, according to age and sex.
The Oxford-AstraZeneca shot was heralded as a “game changer” in the global immunization strategy, Greenberg said in an email. It's cheaper and easier to store and distribute than its rivals.
The latest controversy “presents an enormous challenge for vaccine risk communication,” Greenberg said, and some worry VIPIT — vaccine-induced prothrombotic immune thrombocytopenia — risks sowing another layer of doubt on fertile ground.
Canadians' hesitancy toward COVID-19 vaccines had been softening in recent months. According to polling by the Angus Reid Institute, 66 per cent of 1,748 Canadians sampled in the first week of March said they would get a vaccine as soon as they're eligible rather than take a wait-and-see-approach, up from 39 per cent in September.
“The overall number of Canadians who say they will not be vaccinated,” the pollster reported, “remained stabled, at 12 per cent.”
An Environics Analytics poll found 18 per cent of Canadians aged 16 and older are “unsure” whether they'll get vaccinated, 69 per cent say “yes” and 13 per cent “no.”
Canadians were already more leery about being injected with the Oxford-AstraZeneca vaccine than they were about being inoculated with other approved shots, with a poll by Leger and the Association for Canadians studies conducted over the weekend showing just 53 per cent of respondents expressed trust in the vaccine, far less than 82 per cent who said they'd trust being injected with Pfizer-BioNTech's vaccine or Moderna's (77 per cent).
While people might become more wary of AstraZeneca's shot, as has played out in other countries, Greenberg doesn't think the blood clot scare in Europe (no cases of vaccine-related VIPIT have been reported in Canada) will lead to more vaccine hesitancy here.
“Public fatigue is intense,” he said, fast-spreading variants are driving growing rates of COVID infections, and real-world data showing that Pfizer and Moderna shots are highly effective are increasing public demand for vaccination.
Regulators are in a bind, Greenberg said. “The more transparent they are about communicating what is known about possible risks, the more that could undermine trust in vaccination … But there is no way they can downplay that risk.
“Doing so would play into the hands of anti-vaccination activists who are already peddling misinformation about a conspiracy of silence between governments and the drug manufacturer.”
Toronto and Montreal authorities are already struggling with unfilled vaccine appointments, some longterm care home workers are refusing vaccines and, according to Halifax Today, roughly 20 to 30 per cent of Nova Scotians eligible for the vaccine say they don't plan on getting it. The Lancet Commission on COVID vaccines estimates that halting transmission will ultimately require 70 to 80 per cent coverage.
However, “being hesitant or undecided in the face of a possible safety risk is not being anti-vaccine,” Heidi Larson, director of The Vaccine Confidence Project at the London School of Hygiene & Tropical Medicine, and George Washington University associate professor David Broniatowski wrote in the journal Science. “A failure to understand the distinction can feed both fires.”
The approved COVID vaccines were each tested in tens of thousands of volunteers. However, rare side effects, rare “events,” might not be picked up until many millions receive it, said Dr. Theresa Tam, Canada's chief public health officer.
The rare cases of serious blood clots, including blood clots in the brain, reported by European and Scandinavian countries occur four to 20 days after vaccination, according to a brief from Ontario's COVID-19 Science Advisory Table.
Most cases have been reported in women under 55. It's not clear why, though many countries used most of their initial AstraZeneca supply in women under 55, such as health-care workers.
VIPIT is caused by a “friendly fire” setup, said Dr. Marc Rodger, chair of the department of medicine in the faculty of medicine at McGill University, and physicianin-chief at McGill University Health Centre.
“We develop an antibody response to getting the vaccine that targets a protein called platelet factor 4,” a protein involved in clotting. Clots develop in veins and arteries, causing blurry vision, severe headache, shortness of breath, chest pain, abdominal pain and other symptoms.
“We have to appreciate the first, the index case (the Austrian nurse) that's been published, was vaccinated on February 15. This is all incredibly new,” Rodger said. In the U.K. alone, more than 11 million people have received the AstraZeneca vaccine.
We still don't have a strong handle on the absolute risk. But Rodger said a one-in-100,000-doses risk is similar to the risk of being struck by lightning at some point in a person's lifetime.
“If an 80-year-old has a 30 per cent chance of dying if they get COVID, then I'd take that one in 100,000 risk” of VIPIT, he said. “It looks like it's not a worry in the over55-age group.”