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The dearth of data on seniors in AstraZeneca’s earlier trials is one of the reasons Canada’s NACI briefly recommended the shot not be given to people 65 or older, a decision it reversed in mid-March.

HANNIBAL HANSCHKE/Reuters

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When Canada’s National Advisory Committee on Immunization announced on Monday that it was changing its guidance on the AstraZeneca vaccine for the third time in less than a month, chair Caroline Quach-Thanh conceded the rollout of the shot has been, “like a roller coaster.” Here is the latest, including what you need to know if you’re offered the AstraZeneca vaccine.

Coronavirus tracker: How many COVID-19 cases are there in Canada and worldwide? The latest maps and charts

Why has Canada paused use of the AstraZeneca vaccine for people under the age of 55?

NACI recommended the pause after more data emerged from Europe over the weekend of March 27 and 28 suggesting that an extremely rare and potentially deadly clotting disorder may be linked to the AstraZeneca vaccine.

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In mid-March, more than a dozen European countries temporarily halted use of the shot after a handful of baffling adverse events, some of them fatal, were identified in patients who had recently received the jab.

Unlike common clotting disorders, these cases involved low platelet counts and, in some instances, dangerous clots in a vein in the brain.

European and British drug regulators investigated, and on March 18 they released parallel reports that found no direct link between blood clots and the AstraZeneca vaccine. Canada continued to support the vaccine during the investigations, never suspending its use.

So what changed over the last weekend of March? New German-led research, published online and still undergoing peer review, found the post-vaccination clots were comparable to those caused by a disorder that is known to sometimes occur in reaction to the blood thinner heparin.

In all of the four post-vaccination cases for which the research team had access to blood samples, a test identified antibodies similar to those found in people suffering from the heparin-induced version of the illness. The study team dubbed the new version vaccine-induced prothrombotic immune thrombocytopenia, or VIPIT.

It’s important to note, however, that other experts have argued the German research doesn’t definitively prove the vaccine is to blame.

With scientists having described a plausible mechanism that could link the AstraZeneca shot to the rare clotting disorder, NACI decided to take action. The chief medical officers of health for every province and territory met virtually on Sunday night and agreed to follow NACI’s advice.

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Why has the age cut-off been set at 55?

There are two reasons, both having to do with risk. So far, VIPIT cases in people older than 55 have been extremely rare, despite most of the tens of millions of AstraZeneca doses injected in Europe and Britain going into the arms of seniors.

The risk of serious illness and death due to COVID-19, on the other hand, rises sharply with age. Shelley Deeks, the vice-chair of NACI, told a news conference Monday that it made sense to keep giving the AstraZeneca shot to the population most in danger from the virus, especially with more lethal variants spreading and the third wave escalating.

For people younger than 55, the calculation is more complex. At first, regulators in Europe estimated the risk of the syndrome now known as VIPIT at one case per million vaccinations, Dr. Deeks explained. “As the time has progressed, we’ve seen more cases that have been identified in Europe and the rate has been identified as 1 per 100,000 in Germany,” Dr. Deeks said. “Where the true rate is, we just don’t know at this point in time.”

Of the VIPIT cases that have been identified so far, 40 per cent have been fatal. Given that, Dr. Deeks said NACI decided to err on the side of caution and direct younger people to the mRNA vaccines made by Pfizer-BioNTech and Moderna, neither of which have been associated with the clotting disorder. The mRNA vaccines make up the vast majority of Canada’s supply.

Most cases of clotting have been found in women. Why isn’t Canada giving AstraZeneca to men under 55?

It’s unclear why most of the known cases of VIPIT have occurred in women. It could be because more young women than young men received the AstraZeneca vaccine. Most of the early young recipients were health care workers, a profession that skews female.

“While these reported adverse events have occurred primarily in women, investigations are ongoing as it is possible that more women received the AstraZeneca vaccine, making it difficult to assess risk based on sex,” said Howard Njoo, Canada’s deputy chief public health officer.

Health Canada hasn’t changed the label on the vaccine to match NACI’s advice. Why not?

Supriya Sharma, Health Canada’s chief medical adviser, said the regulator is still investigating. Health Canada has asked AstraZeneca to provide a new risk-benefit analysis for the shot, broken down by age group and gender.

On March 24, Health Canada updated the product monograph – the vaccine’s official label – to provide information on the very rare risk of clots potentially associated with the shot. The changes apply to both the regular AstraZeneca product and a nearly identical product made in India, known as Covishield.

Dr. Sharma pointed out that other regulators, including the European Medicines Agency, have not changed the label regarding age either, even though public-health officials in some European countries have made recommendations similar to NACI’s. France is recommending it for people 55 and older, and Sweden for those 65 and up. Norway, Denmark and Finland, meanwhile, have suspended use of the AstraZeneca vaccine for all ages.

How has the AstraZeneca vaccine performed in the real world?

Very well. Developed in partnership with Oxford University, the AstraZeneca jab has been the workhorse of Britain’s successful vaccination drive. As a result, the bulk of the real-world data on the shot’s effectiveness come from Britain.

Public Health England continues to publish regular updates on how effective COVID-19 vaccines are proving, and the AstraZeneca shot has helped to cut cases, hospital admissions and deaths significantly, including those caused by the B.1.1.7 variant, a version of the coronavirus that is now spreading quickly in Canada.

One notable exception arose in South Africa, where the government halted use of the vaccine when preliminary results showed it wasn’t making much of a difference in preventing mild disease. Like other vaccines, the AstraZeneca shot doesn’t work as well against B.1.351, the dominant variant in South Africa, as it does against B.1.1.7 and earlier versions of the coronavirus.

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16/16

14/14

11/11

How the oxford-AstraZeneca

vaccine works

Spike

protein

Spike protein:

Gene is cut from

Sars-CoV-2 genome

Virus

genome

Gene: Inserted into DNA

of adenovirus which acts

as vector in vaccine

Gene

Adenovirus:

Unable to

cause disease

Vaccine: Induces spike

protein antigen – triggers

antibody immune response

Antibodies

Human immune

system: Produces

antibodies against

spike proteins

Vaccine: Can be

stored in refrigerator

at 2 to 8°C. Two doses

of vaccine are

required

graphic news, SOURCE: Reuters; Oxford

Vaccine Trial; University of Oxford

16/16

14/14

11/11

How the oxford-AstraZeneca

vaccine works

Spike

protein

Spike protein:

Gene is cut from

Sars-CoV-2 genome

Virus

genome

Gene: Inserted into DNA

of adenovirus which acts

as vector in vaccine

Gene

Adenovirus:

Unable to

cause disease

Vaccine: Induces spike

protein antigen – triggers

antibody immune response

Antibodies

Human immune

system: Produces

antibodies against

spike proteins

Vaccine: Can be

stored in refrigerator

at 2 to 8°C. Two doses

of vaccine are

required

graphic news, SOURCE: Reuters; Oxford Vaccine Trial;

University of Oxford

18/18

16/16

13/13

How the oxford-AstraZeneca vaccine works

Spike protein

Adenovirus:

Unable to

cause disease

Gene

Virus genome

Spike protein:

Gene is cut from

Sars-CoV-2 genome

Gene: Inserted into DNA

of adenovirus which acts

as vector in vaccine

Antibodies

Vaccine: Induces spike

protein antigen – triggers

antibody immune response

Human immune

system: Produces

antibodies against

spike proteins

Vaccine: Can be

stored in refrigerator

at 2 to 8°C. Two doses

of vaccine are required

graphic news, SOURCE: Reuters; Oxford Vaccine Trial; University of Oxford

Why hasn’t the U.S. approved the AstraZeneca shot?

Before the U.S. Food and Drug Administration would consider approval, the regulator asked the company to conduct a larger clinical trial primarily in the United States, one that enrolled more seniors than did AstraZeneca’s earlier trials. (The dearth of data on seniors in AstraZeneca’s earlier trials is one of the reasons Canada’s NACI briefly recommended the shot not be given to people 65 or older, a decision it reversed in mid-March.)

Controversy erupted when AstraZeneca finally released the results of the U.S. trial last week.

In a press release March 22, the British-Swedish company said the trial, which enrolled more than 32,000 participants in the U.S., Chile and Peru, found two doses of the vaccine given four weeks apart to be 79-per-cent efficacious against symptomatic disease and 100-per-cent efficacious in preventing COVID-19 hospital admissions and deaths.

Less than 24 hours later, the U.S. National Institute of Allergy and Infectious Diseases issued an extraordinary middle-of-the-night statement saying the independent scientists monitoring the trial were concerned the data in the press release were outdated and possibly misleading. AstraZeneca revised its conclusions two days later to say the vaccine was 76-per-cent efficacious against symptomatic COVID-19.

Company officials are expected to receive a grilling when they appear before an FDA advisory committee that makes recommendations on vaccine approvals. A date for the meeting, a precursor to approval, has not yet been set.

What will happen to Canada’s AstraZeneca supply, including a new shipment of 1.5 million doses from the U.S.?

Provinces are continuing to roll out the vaccine to people 55 and over, and they plan to do the same with doses that arrived from the U.S. Tuesday as part of a loan arrangement. NACI, Health Canada and chief medical officers of health for every province all say the benefits of the shot continue to outweigh the risks for older people.

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The same advice applies to Covishield, which is so far the only version of the AstraZeneca shot to be injected in Canada. The federal government received 500,000 doses of the product from India in March; a little over 300,000 of those have been injected so far.

If I’m younger than 55 and I’ve already received a first dose of AstraZeneca, what should I do about my second shot?

Wait for advice from NACI and Health Canada. Dr. Njoo said Monday that more definitive information should be available by the time recipients are due for their second doses, which NACI has advised be given as far apart as four months as part of a “first doses fast” strategy.

There is a possibility that Canadians may be permitted to mix and match their first and second doses, but that depends on the results of international trials. Britain is studying a mix-and-match strategy. Findings could be available as early as June or July, Dr. Sharma said.

If I do decide to take the AstraZeneca vaccine, how can I monitor myself for signs of VIPIT?

VIPIT is so rare that no cases of it have yet been identified in Canada. Based on Europe’s limited experience, Health Canada has advised vaccine recipients and their doctors to watch out for any of the following symptoms four to 16 days after receiving the shot: Shortness of breath, chest pain, leg swelling, persistent abdominal pain, sudden onset of severe and worsening headaches, and skin bruising in places other than the injection site. McMaster University in Hamilton is prepared to test for the syndrome, which can be successfully treated if caught in time.

The large number of COVID-19 infections in some places makes it more likely for new variants of the virus to emerge. Science Reporter Ivan Semeniuk explains how vaccines may not be as effective against these new strains, making it a race to control and track the spread of variants before they become a dangerous new outbreak. The Globe and Mail

With a report from Ivan Semeniuk

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