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

Nav Canada will not be closing the tower at West Kootenay Regional Airport. Photo: Betsy Kline
Nav Canada tower to remain open at West Kootenay Regional Airport

The organization was considering closing the tower

Dresses hang outside Nelson city hall as part of the REDress Project by Métis artist Jaime Black. Photo: Bill Metcalfe
Nelson’s REDress Project exhibit vandalized

The REDress Project brings attention to missing and murdered Indigenous women

A woman wears a protective face covering to help prevent the spread of COVID-19 as she walks past the emergency entrance of Vancouver General Hospital in Vancouver, B.C., Friday, April 9, 2021. THE CANADIAN PRESS/Jonathan Hayward
54 more cases of COVID-19 in Interior Health

Thirty-two people in the region are in hospital with the virus, 11 of them in intensive care

Dr. Katherine Oldfield is a naturopathic physician, mother, and active member of the Nelson-West Kootenay chapter of Citizens’ Climate Lobby. Photo: Submitted
COLUMN: Restore our Earth, restore our health

Katherine Oldfield marks Earth Day by writing about the priorities we need to have

Canadian Prime Minister Justin Trudeau and United States President Joe Biden smile as they say farewell following a virtual joint statement in Ottawa, Tuesday, February 23, 2021. THE CANADIAN PRESS/Adrian Wyld
Trudeau pledges to cut emissions by 40% to 45% by 2030, short of U.S. goal

Trudeau announced target during a virtual climate summit convened by U.S. President Joe Biden

Journal de Montreal is seen in Montreal, on Thursday, April 22, 2021. The daily newspaper uses a file picture of Prime Minister Justin Trudeau dressed in traditional Indian clothing during his trip to India to illustrate a story on the Indian variant of the coronavirus. Paul Chiasson/The Canadian Press
Montreal newspaper blasted for front-page photo of Trudeau in India

Trudeau is wearing traditional Indian clothes and holding his hands together in prayer beside a caption that reads, ‘The Indian variant has arrived’

Nanaimo RCMP say a man was injured while pouring gunpowder on a backyard fire in Harewood on Wednesday, April 21. (File photo)
Nanaimo man hospitalized after pouring gunpowder onto backyard fire

RCMP investigating explosion in Harewood also came across a still for making alcohol on property

Provincial health officer Dr. Bonnie Henry arrives for briefing on the COVID-19 situation, B.C. legislature, Oct. 26, 2020 (B.C. government)
B.C. sees 1,006 COVID-19 cases Thursday, ‘alarming’ 502 in hospital

Vaccine bookings for people aged 60 and older set to start

Shannon Zirnhelt, from left, her son Lockie, 3, Julia Zirnhelt, 13, and Ella Krus, 13, co-founders of Third Planet Crusade are featured in a music video set to air on Earth Day, April 22, 2021. (Monica Lamb-Yorski photo - Williams Lake Tribune)
B.C.-made music video launched in time for Earth Day 2021

Singer songwriter Shannon Zirnhelt worked with Third Planet Crusade on the project in the Cariboo

Ambulance crews have been busy with a record number of emergency overdose calls this Wednesday, April 21. (BC Emergency Health Services)
B.C. paramedics responded to a record 138 overdose calls in a single day

Wednesday’s calls included 48 in the Vancouver Coastal Health region and 51 in Fraser Health

B.C. Health Minister Adrian Dix and Premier John Horgan describe vaccine rollout at the legislature, March 29, 2021. (B.C. government)
B.C. COVID-19 hotspots targeted as AstraZeneca vaccine runs low

17,000 appointments booked the first day for people aged 40 and up

A nurse loads a syringe with a vaccine for injection at the Victoria Clipper Terminal. THE CANADIAN PRESS/Chuck Stoody
B.C.’s COVID-19 vaccine rollout not enough to bring back normal life by fall: report

Only 51% of the population will be protected under B.C.’s current rollout, SFU professors say more vaccinations are needed to achieve herd immunity

Most Read