Canadian authorities recommended Monday a halt on administering the AstraZeneca PLC Covid-19 vaccine on people under the age of 55 in light of evidence from Europe on potentially serious side effects targeting younger women.
The change in guidance marked a sharp shift from Canadian health officials, who up until now have said the AstraZeneca vaccine was safe for people of all ages -- a point they emphasized earlier this month when governments in Europe paused the vaccine's use amid worries over blood clotting. This also marks the latest setback for the British-Swedish drugmaker, which has faced pushback from governments, regulators and the public about the rollout of its vaccine.
Health Canada, the country's drug regulator, has ordered AstraZeneca to conduct a detailed risk-benefit analysis on the vaccine by age and gender. The information, officials said, would help determine whether specific demographic groups might be at higher risk.
Canadian officials said the change in guidance on AstraZeneca stems from the emergence of additional reports of blood clotting in people who received the vaccine in Europe. Some European cases were reviewed in a recent preprint research paper that focused on nine patients in Germany and Austria. The findings from the preprint were first reported by researchers earlier this month.
The preprint research looked at nine patients whose ages ranged from 22 to 49 and who had developed thrombosis, which occurs when a blood clot forms inside a blood vessel, beginning four to 16 days after getting the AstraZeneca vaccine. Eight of the patients were female. Four of the nine patients died.
The paper refers to blood clotting after a Covid-19 vaccination as a rare adverse effect, and one that has so far only been reported in patients who received the AstraZeneca vaccine.
Canadian officials said that, based on information from Europe, the incident rate was originally estimated at one per one million people vaccinated with the AstraZeneca vaccine, but a higher rate of one in 100,000 was later reported by researchers in Germany. Among the people who developed blood clotting after receiving the vaccine, the fatality rate is estimated at 40%, the officials said.
Considering this information and knowing that Canada has authorized three other Covid-19 vaccines, "there is substantial uncertainty about the benefit of providing AstraZeneca Covid-19 vaccine to adults under 55 years of age given the potential risk," said Dr. Shelley Deeks, vice chairwoman of the National Advisory Committee on Immunization, an independent panel of scientists.
The panel's recommendations aren't binding. At least two Canadian provinces, which are responsible for carrying out Covid-19 vaccinations, said they were immediately halting use of the AstraZeneca shot on younger people.
"This is a pause while we wait for more information to better understand what we are seeing in Europe," said Dr. Joss Reimer, head of Manitoba's vaccine task force. "We have to respond to what we know, when we know it, in this vaccine campaign."
An AstraZeneca spokesman said the company respects the decision from the immunization advisory panel. He added that Health Canada still deems the vaccine safe for use, and an "extensive body of data from two large clinical data sets and real-world evidence demonstrate its effectiveness, reaffirming the role the vaccine can play during this public health crisis."
Canada authorized use of the AstraZeneca vaccine, created in partnership with the University of Oxford, on Feb. 26. Health Canada -- which has oversight on drugs -- has said the benefits of the vaccine outweighed any risks and stuck to that position while European countries paused AstraZeneca's use because of concerns about the risk of blood clotting in older people. The European Union's health agency later determined the shot was safe and effective and didn't increase the risk of blood clots.
Dr. Supriya Sharma, senior medical adviser at the country's health department, said last week that reports of blood clots after vaccination were rare, but their unusual nature warranted further investigation. She said Health Canada would review evidence about the blood clots as it becomes available and would take action if new safety issues are confirmed.
On Monday, Dr. Sharma said she supported the recommendation, while adding that the AstraZeneca vaccine will still remain effective in preventing hospitalizations and deaths for people 55 and over, or those most susceptible to Covid-19's fallout. "It's reasonable to pause for a period of time while this [risk] continues to be evaluated," she said. "I fully understand this can be confusing. Especially for this vaccine, which has had a lot of confusion surrounding it."
To date, officials said about 300,000 Canadians have received a shot of the AstraZeneca vaccine. Canada authorized use of AstraZeneca's shot in late February, whereas in the U.S. the vaccine remains under review. It is rare for Health Canada to get so out in front of the Food and Drug Administration on drug authorization, said Mark Warner, a lawyer who practices in Canada and the U.S. who has advised pharmaceutical companies.
"That choice and the continuing noise around the AstraZeneca vaccine has led to some predictable confusion in the rollout of the vaccine in Canada," he said.
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