Canada’s National Advisory Committee on Immunization is giving the Oxford-AstraZeneca COVID-19 vaccine the green light to be used on adults who are 65 or older. (AP Photo/Frank Augstein)

Canada’s National Advisory Committee on Immunization is giving the Oxford-AstraZeneca COVID-19 vaccine the green light to be used on adults who are 65 or older. (AP Photo/Frank Augstein)

How effective is the AstraZeneca COVID-19 vaccine? What Canadians need to know

Here’s what we know about the AstraZeneca vaccine:

Canada’s National Advisory Committee on Immunization is giving the Oxford-AstraZeneca COVID-19 vaccine the green light to be used on adults who are 65 or older.

That decision comes two weeks after NACI said there wasn’t enough evidence from clinical trials to show whether the AstraZeneca jab was as effective in older populations.

Health experts who disagreed with NACI’s March 1 decision pointed to real-world data suggesting the shot was safe and effective among the elderly. Countries like France and Germany, who previously said they wouldn’t offer AstraZeneca to those over 65, recently reversed their decisions.

Those countries, and several others around Europe, have since paused the use of AstraZeneca for another reason — reports of blood clots among some recipients after receiving the jab. European regulators say there’s no evidence the shot is to blame, however.

AstraZeneca’s vaccine was the third to be approved by Health Canada, joining Pfizer-BioNTech and Moderna in late February. Canada has since authorized a fourth vaccine by Johnson & Johnson.

Here’s what we know about the AstraZeneca vaccine:

HOW EFFECTIVE IS IT?

Data from clinical trials showed AstraZeneca was 62 per cent effective in preventing COVID infections, but it also prevented death and hospitalization in all participants who got the virus after receiving the vaccine.

Efficacy was a major talking point when AstraZeneca was first approved, with some comparing it to the 95 per cent efficacy shown in mRNA vaccine trials from Pfizer and Moderna. But experts have stressed that all the authorized vaccines offer excellent protection against severe disease.

Dr. Zain Chagla, an infectious disease expert with McMaster University, says when dosing regimens are factored in, AstraZeneca’s efficacy rises to “70 to 80 per cent by the second dose, which is comparable to Pfizer, Moderna and Johnson & Johnson.”

Real-world data is emerging that may also suggest the efficacy of AstraZeneca’s vaccine increases over a longer time interval between the first and second shot. Clinical trials used a four-week span between doses but some countries have been delaying second doses by several weeks.

DOES IT WORK AGAINST THE NEW VARIANTS?

AstraZeneca’s vaccine had some promising data last month suggesting it works against the variant first detected in the U.K. Findings based on swabs taken from around 500 volunteers in trials between October and January showed a 74.6 per cent efficacy rate against that variant.

A group of experts on immunization working with the World Health Organization recommended the use of AstraZeneca’s vaccine in February, even in countries where variants have emerged as dominant.

That guidance came after a small study in South Africa suggested AstraZeneca’s vaccine was only minimally effective against the variant first detected there, causing the country to halt use of the product.

WHAT ABOUT THE BLOOD CLOT ISSUE?

A number of AstraZeneca recipients in Europe have reported blood clots after getting the jab, casting doubt on its safety. But a European Union medicine regulator said Tuesday there was “no indication” that AstraZeneca’s vaccines are causing the reported clots.

Dr. Lynora Saxinger, an infectious disease specialist with the University of Alberta, says a blood clot, or a pulmonary embolism, is “an incredibly common thing.”

Saxinger said she would need to see more information about the blood clots that are being reported, such as how old the recipients are. But numbers of those reporting the clots should also be seen in the context of how many people get the vaccine and don’t report that side effect, she added.

“We did not see any signal of (blood clots) in the trials of the vaccine, which had tens of thousands of people in them,” Saxinger said.

Chagla says data suggests the number of those reporting blood clots is well within the normal range experts would expect to see in a given population, meaning they may have happened in those people whether they got the vaccine or not.

AstraZeneca said over the weekend that a review of 17 million patients who received the shot in Europe and the U.K. shows no elevated risk of blood clotting.

Prime Minister Justin Trudeau offered reassurances on the safety of the AstraZeneca vaccine on Monday, saying Health Canada regulators are constantly analyzing all the available information and have guaranteed that the inoculations approved in Canada are safe for use.

HOW DOES THE VACCINE WORK?

Unlike Pfizer-BioNTech and Moderna, which use messenger RNA (mRNA), the AstraZeneca vaccine is a non-replicating viral vector, using a weakened chimpanzee cold virus as a vessel.

Scientists stripped the genes from that virus, which isn’t harmful to humans, and replaced them with the spike protein gene for SARS-CoV-2.

Once injected, the vaccine shows our bodies how to produce the immune response needed to ward off future infections from the COVID-19 virus.

Some may see outward signs of an immediate immune response to the vaccine — the body’s way of preparing for what it perceives as an attack by the virus. This can cause side effects usually seen with other vaccines, including pain at the injection site, redness, swelling and even fever, but experts say that means the vaccine is working.

Coronavirusvaccines

Get local stories you won't find anywhere else right to your inbox.
Sign up here

Just Posted

Image/ Metro Creative Connection
County of Wetaskiwin responds to Alberta Energy Regulator’s decision on Directive 067.

On April 7, 2021 the Alberta Energy Regular (AER) announced a new edition of Directive 067.

A damaged unicorn statue is shown in a field outside of Delia, Alta. in this undated handout photo. It’s not often police can report that a unicorn has been found, but it was the truth Saturday when RCMP said a stolen, stainless-steel statue of the mythical beast had been located in a field not far from where he’d been taken. THE CANADIAN PRESS/HO, RCMP *MANDATORY CREDIT*
Mounties get their unicorn; stolen statue of mythical beast found in Alberta field

Police are still looking for suspects, and have called in their forensics experts to help

There were six additional deaths across Alberta reported over the past 24 hours, bringing the death toll to 1,926 since the beginning of the pandemic. (File photo)
file photo
Wetaskiwin RCMP respond to break and enter and theft at a Wetaskiwin church

RCMP responded to a break and enter and theft at Jesus Cares Fellowship Church.

Each spring, the Okanagan Fest-of-Ale is held in Penticton. This year, as a result of the COVID-19 pandemic, the festival will not be held. However, beer is still available. How much do you know about this beverage? (pxfuel.com)
QUIZ: How much do you really know about beer?

Put your knowledge to the test with this short quiz

Pall Bearers carrying the coffin of the Duke of Edinburgh, followed by the Prince of Wales, left and Princess Anne, right, into St George’s Chapel for his funeral, at Windsor Castle, in Windsor, England, Saturday April 17, 2021. (Danny Lawson/Pool via AP)
Trudeau announces $200K donation to Duke of Edinburgh award as Prince Philip laid to rest

A tribute to the late prince’s ‘remarkable life and his selfless service,’ the Prime Minister said Saturday

A vial of some of the first 500,000 AstraZeneca COVID-19 vaccine doses that Canada secured. THE CANADIAN PRESS/Carlos Osorio
Canada’s 2nd blood clot confirmed in Alberta after AstraZeneca vaccine

The male patient, who is in his 60s, is said to be recovering

The funeral of Britain’s Prince Philip in Windsor, England, on Saturday, April 17, 2021. Philip died April 9 at the age of 99. (Kirsty Wigglesworth/AP)
PHOTOS: Prince Philip laid to rest Saturday as sombre queen sits alone

The entire royal procession and funeral took place out of public view within the grounds of Windsor Castle

Prime Minister Justin Trudeau looks on as Deputy Prime Minister and Finance Minister Chrystia Freeland responds to a question during a news conference on Parliament Hill in Ottawa, Tuesday, Aug. 18, 2020. THE CANADIAN PRESS/Adrian Wyld
Expectations high as Trudeau Liberals get ready to unveil first pandemic budget

The Liberals will look to thread an economic needle with Monday’s budget

Doses of the Moderna COVID‑19 vaccine in a freezer trailer, to be transported to Canada during the COVID-19 pandemic. THE CANADIAN PRESS/Nathan Denette
Pfizer to increase vaccine deliveries in Canada as Moderna supply slashed

Moderna plans to ship 650,000 doses of its vaccine to Canada by the end of the month, instead of the expected 1.2 million

A empty classroom is pictured at Eric Hamber Secondary school in Vancouver, B.C. Monday, March 23, 2020. The Alberta government says schools in Calgary will move to at-home learning starting Monday for students in grades 7 to 12.THE CANADIAN PRESS/Jonathan Hayward
Calgary schools to shift to at-home learning for grades 7 to 12 due to COVID-19

The change, due to COVID-19, is to last for two weeks

Most Read