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

A man was sentenced to more than a year in jail for a late-night robbery in Courtenay last April. Photo by Mike Chouinard
Late-night Courtenay robbery results in 500-plus days in jail

Heatley’s sentence also includes probation, DNA order, firearms ban

A 3.0-magnitude earthquake occurred off Ucluelet just after 12:30 a.m. on April 10 and was reportedly felt as far south as Oregon. (Map via United States Geological Survey)
Quake off Ucluelet reportedly felt as far south as Oregon

Magnitude 1.5 earthquake also reported off Vancouver Island’s west coast hours earlier

The CSRHD board has diverging views on its relationship with Island Health. File photo
Comox-Strathcona board ponders relationship with Island Health

“We have to stand together … to get our share of the health budget.”

The CVCDA Accessibility Project is creating safer ramps at the Courtenay facility. Photo supplied
Accessibility project underway at Comox Valley Child Development Association

Over the past month, you may have noticed some construction underway behind… Continue reading

B.C. Health Minister Adrian Dix and Premier John Horgan describe vaccine rollout at the legislature, March 29, 2021. (B.C. government)
1,262 more COVID-19 infections in B.C. Friday, 9,574 active cases

Province’s mass vaccination reaches one million people

Cannabis bought in British Columbia (Ashley Wadhwani/Black Press Media)
Is it time to start thinking about greener ways to package cannabis?

Packaging suppliers are still figuring eco-friendly and affordable packaging options that fit the mandates of Cannabis Regulations

Two-year-old Ivy McLeod, seen here on April 9, 2021 with four-year-old sister Elena and mom Vanessa, was born with limb differences. The family, including husband/dad Sean McLeod, is looking for a family puppy that also has a limb difference. (Jenna Hauck/ Chilliwack Progress)
B.C. family looking for puppy with limb difference, just like 2-year-old Ivy

Ivy McLeod born as bilateral amputee, now her family wants to find ‘companion’ puppy for her

A vehicle that was driven through the wall of a parkade at Uptown Shopping Centre and into the nearby Walmart on April 9 was removed through another hole in the wall later that night. (Photo via Saanich Police Department and Ayush Kakkar)
Vehicle launched into B.C. Walmart removed following rescue of trapped workers

Crews cut new hole in parkade wall to remove vehicle safely

Four members with Divers for Cleaner Lakes and Oceans were out at Cultus Lake on March 28 and 29 hauling trash out of the waters. (Henry Wang)
PHOTOS: Out-of-town divers remove 100s of pounds of trash from Cultus Lake

Members of Divers for Cleaner Lakes and Oceans hauled out 470 pounds of trash over two days

As of Saturday, April 10, people born in 1961 are the latest to be eligible for a COVID-19 vaccine. (Black Press files)
B.C. residents age 60+ can now register to get their COVID-19 vaccine

Vaccine registration is now open to people born in 1961 or earlier

A new saline gargle test, made in B.C., will soon be replacing COVID-19 nasal swab tests for kids. (PHSA screenshot)
Take-home COVID-19 tests available for some B.C. students who fall ill at school

BC Children’s Hospital plans to provide 1,200 kits to Vancouver district schools this April

Ruming Jiang and his dog Chiu Chiu are doing fine following a brush with hypothermia that saw several people work together to get them out of the Fraser River near Langley’s Derby Reach Park on March 25, 2021 (Special to the Advance Times)
Man finds men who rescued him from drowning in B.C.’s Fraser River

A grateful Ruming Jiang says he will thank them again, this time in person when the pandemic ends

The 10-part Netflix series Maid, which is being exclusively shot in Greater Victoria, was filming near Prospect Lake in Saanich last month. (Photo courtesy Fred Haynes)
Province announces $150,000 towards South Island film studio, fulfilling B.C. NDP promise

Investment to fund movie studio feasibility study at Camosun College

Most Read