Why Canada is suspending use of AstraZeneca vaccine in people under 55

Canada's vaccine advisory committee is recommending immediately suspending the use of the AstraZeneca-Oxford COVID-19 vaccine in Canadians under 55 following reports of rare but potentially fatal blood clots in Europe that appear to be connected to the shot.

The National Advisory Committee on Immunization (NACI) updated its guidelines to provinces and territories against the use of the vaccine for younger Canadians on Monday over safety concerns.

Health Canada said Monday that 300,000 doses of AstraZeneca vaccine have been administered and no cases of the rare blood clotting adverse events have been reported in Canada, but that it was aware of additional cases that have recently been reported in Europe.

Quebec, Ontario, Alberta, Saskatchewan, Manitoba, Newfoundland and Labrador and Prince Edward Island have all suspended the use of the vaccine for anyone below the age of 55. Other provinces and territories are expected to follow.

Dr. Isaac Bogoch, an infectious diseases physician and member of Ontario's COVID-19 vaccine task force said that the discovery of a potential connection with the vaccine to blood clots raised a "red flag" that "warrants further exploration."

"People should appreciate that not all blood clots are created the same," he said. "This is a very specific and particular method of blood clotting that likely has an association with the vaccine."

Risk of blood clots seems not to affect older age groups: NACI

NACI previously recommended earlier this month that Canadians over 65 not receive the shot, despite emerging evidence from around the world demonstrating its ability to prevent severe COVID-19 in older adults.

But that guidance changed on March 16 after more real-world data on the vaccine's effectiveness was reviewed by NACI, and CBC News broke the story revealing documents on the federal government's plans to allow those 65 and older to receive it.

"This vaccine has had all the ups and downs — it looks like a roller coaster," said Dr. Caroline Quach, chair of NACI and a pediatric infectious diseases expert. "The problem is because data are evolving, we are also evolving our recommendations."

Quach said the risk of rare blood clots appears to only occur in younger populations, which is why NACI recommended suspending the vaccine in those under 55.

"What we're doing is trying to contrast the risks and benefits," she said. "So if you have that vaccine versus having to wait for two months while COVID is ramping and you're at risk of catching it and having complications from it, I think that taking the vaccine is the best option at this point."

Quach added that the vaccine works well in preventing severe outcomes and death in older populations over 55, particularly in those over 70, and the risk of blood clots does not appear to be present in those age groups.

WATCH | Canada pauses use of AstraZeneca vaccine in people under 55:

"What we need to have is continued confidence in our expert review panel that it's looking at these vaccines and deciding what is going to be best, safest and most effective for Canadians," said Alyson Kelvin, an assistant professor at Dalhousie University and virologist at the Canadian Center for Vaccinology in Halifax.

"This is a new vaccine to a new virus, it's really important that we're following all the data as closely as possible and as the vaccines are rolling out, we're understanding them more and reviewing what the guidance should be."

Dr. Zain Chagla, an infectious diseases physician at St. Joseph's Healthcare Hamilton and an associate professor at McMaster University, said NACI is taking a calculated risk by recommending older Canadians still get the vaccine because they are at higher risk of severe outcomes from COVID-19.

"Scientifically, it makes sense," he said. "This isn't saying that everyone under 55 is going to get this complication. It's the slight risk of this complication seems to be more predisposed in this age group. But again, the raw numbers seem to be very, very low."

What led to Canada's decision to suspend AstraZeneca

The decision to halt the use of the vaccine in Canadians under 55 comes after the European Medicines Agency (EMA) investigated 25 cases of the rare blood clots out of about 20 million AstraZeneca shots given. It concluded on March 18 that the benefits from the vaccine far outweigh its possible risks, although a definitive link could not be ruled out.

But 18 of the cases in Europe were of an extremely rare type of blood clot called cerebral venous sinus thrombosis (CVST) — where veins that drain blood from the brain are obstructed and can potentially cause fatal bleeding.

The EMA said on March 18 at least nine deaths have been associated with the adverse events in Europe and the agency is continuing to investigate the situation.

Germany's medical regulator told The Associated Press on Monday it had received reports of 21 cases of rare blood clots in people who had recently received AstraZeneca's coronavirus vaccine.

The Paul Ehrlich Institute also said that seven people affected by the blood clots have died. It added that of the 21 cases reported in Germany until March 25, 12 also involved an abnormally low level of platelets in the patients' blood.

Nineteen of the 21 cases were in women ages 20 to 63, while two were in men ages 36 and 57. During the period covered by the reports, some 2.27 million first doses of the AstraZeneca vaccine were administered in Germany.

"You cannot ignore the blood clots that have been associated with AstraZeneca globally," said Bogoch. "It's not entirely clear what the true incidence of this is, but it does appear to be a rare event."

What Canadians need to know about the AstraZeneca vaccine

The federal health ministry said it would be requiring both manufacturers, AstraZeneca and India's Serum Institute, to conduct risk assessments by age and gender — but is requesting more data before deciding whether or not to change authorization of it in Canada.

Health Canada had previously updated the vaccine's label with information on the rare blood clotting events.

Canadian health officials said during a press conference Monday the specific syndrome is being called Vaccine-Induced Prothrombotic Immune Thrombocytopenia (VIPIT) and that they are in contact with European officials about it.

"I do understand why Canadians might feel worried," said Canada's Deputy Chief Public Health Officer Dr. Howard Njoo.

"What I can say is that the chief medical officers of health of the provinces and territories take vaccine safety very seriously and we want Canadians to have confidence in these vaccines."

Officials added that Germany's Paul Ehrlich Institute reported VIPIT has an incidence rate of about one in 100,000, with a mortality rate of about 40 per cent, although more research is needed and that risk is reduced if treated early enough.

"Where the true rate is, we just don't know at this point in time," said NACI Co-Chair Dr. Shelley Deeks. "But we are continuing to follow the data, as it emerges."

Symptoms to watch for

The Public Health Agency of Canada released a statement on Monday saying that "there is no cause for concern" for Canadians who have already been vaccinated with AstraZeneca for more than 20 days, but that you should seek immediate medical attention in the rare event you develop the following symptoms four or more days after vaccination:

• Shortness of breath.

• Chest pain.

• Leg swelling.

• Persistent abdominal pain.

• Sudden onset of severe or persistent worsening headaches or blurred vision.

• Skin bruising (other than at the site of vaccination).

PHAC said decisions on the type of second dose that will be offered to those who have been vaccinated with AstraZeneca will be determined based on the "latest evidence and research."

Most of the complications in Europe occurred within 14 days of receiving the AstraZeneca shot, and the majority were in women under the age of 55. It's worth noting that CVST is typically more common in women, particularly during and after pregnancy, while on birth control and hormone replacement therapy.

Germany and Italy resumed vaccinations with the shot on March 19, but France opted to vaccinate only those over 55 with it after discovering several cases of CVST. Denmark and Norway have suspended the use of the vaccine altogether for at least three weeks, while Sweden has resumed the use of the vaccine in those over 65.

"The real question here is, how common is it, and are there identifiable risk factors for this? That way, we could probably continue to use this vaccine in people with very, very low risks of having a blood clot and selectively vaccinate people who would benefit," Bogoch said.

"If there is that risk, we would hopefully have better data to support who we could safely and selectively vaccinate with this product."

Benefits still outweigh risks, says vaccine maker

A spokesperson for AstraZeneca Canada said in a statement the company respects the decision by NACI but stressed that Health Canada's guidance to health care providers around the use of the vaccine remains unchanged.

"Regulatory authorities in the U.K., European Union, the World Health Organization and Health Canada have concluded that the benefits of using our vaccine to protect people from this deadly virus significantly outweigh the risks across all adult age groups," the statement read.

"Tens of millions of people have now received our vaccine across the globe. The 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."

Chagla said NACI's decision will likely hurt confidence in the vaccine in the eyes of Canadians, especially among those over 55 who may be left "scratching their heads" as to why the vaccine is being recommended for their age group but not younger people.

"I, unfortunately, envision this vaccine is going to have a limited rollout in Canada moving forward," he said.

"Even if the dust starts settling, and it's a completely separate issue or it's much lower risk than expected, I don't think you're going to get many under 55-year-olds to get this vaccine anymore ,and that's the reality."