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 Quesnel resident receives a shot of the Moderna COVID-19 vaccine earlier this month. (Photo credit: Cassidy Dankochik/Quesnel Cariboo Observer)
IH says COVID-19 vaccines safe despite claims of Lytton physician

Doctor makes unsubstantiated claims about serious side effects of Moderna vaccine

People are shown at a COVID-19 vaccination site in Montreal, Sunday, April 18, 2021, as the COVID-19 pandemic continues in Canada and around the world. THE CANADIAN PRESS/Graham Hughes
211 new COVID-19 cases in Interior Health over the weekend

Currently, there are 875 active cases of the virus in the region

A nurse prepares a dose of the COVID-19 vaccine in Kelowna on Tuesday, March 16. As of April 19, more than 230,000 doses have been administered across the Interior Health region. (Phil McLachlan/Black Press)
More than 230K doses of COVID-19 vaccine administered across Interior Health

A total of 220,216 first doses and 13,775 second doses have been given to residents across the B.C. Interior

B.C. homeowners are being urged to take steps to prepare for the possibility of a flood, this includes protecting one’s home by moving equipment and other assets from these areas to higher ground. (J.R. Rardon)
‘Entire province faces risk’: B.C. citizens urged to prepare for above-normal spring flood season

High-streamflow advisory issued for the Cariboo Region and areas including Williams Lake, Quesnel and Prince George

Elvira D’Angelo, 92, waits to receive her COVID-19 vaccination shot at a clinic in Montreal, Sunday, March 7, 2021, as the COVID-19 pandemic continues in Canada and around the world. THE CANADIAN PRESS/Graham Hughes
110 new cases of COVID-19 in Interior Health

Provincial health officers announced 1,005 new cases throughout B.C.

In this image from NASA, NASA’s experimental Mars helicopter Ingenuity lands on the surface of Mars Monday, April 19, 2021. The little 4-pound helicopter rose from the dusty red surface into the thin Martian air Monday, achieving the first powered, controlled flight on another planet. (NASA via AP)
VIDEO: NASA’s Mars helicopter takes flight, 1st for another planet

The $85 million helicopter demo was considered high risk, yet high reward

(Photo by Mojpe/Pixabay)
Canadian kids extracting record amounts from Tooth Fairy

Our neighbours in the U.S. receive slightly less from Tooth Fairy visits

Families of two of three workers killed in a train derailment near Field, B.C., in 2019 have filed lawsuits accusing Canadian Pacific of gross negligence. The derailment sent 99 grain cars and two locomotives off the tracks. THE CANADIAN PRESS/Jeff McIntosh
Families of workers killed in Field train derailment allege negligence in lawsuit

Lawsuits allege the workers weren’t provided a safe work environment

(New Westminster Police)
4 youth arrested after 30-person brawl in New Westminster leaves 1 seriously injured

Police are looking for witnesses who saw the incident take place

South Surrey’s Paul Cottrell, who works with the DFO, tows a grey whale out of Semiahmoo Bay Sunday. (Contributed photo)
Dead whale floating near White Rock towed to shore for necropsy

Animal has been dead since at least April 15

Sunday’s storm rocked one of the ferries crossing Kootenay Lake. Photo: Dirk Jonker
VIDEO: Storm makes for wild ferry ride across Kootenay Lake

The video was captured by ferry employee Dirk Jonker

Dr. Bonnie Henry gives her daily media briefing regarding Covid-19 for the province of British Columbia in Victoria, B.C, Monday, December 7, 2020. THE CANADIAN PRESS/Jonathan Hayward
Toddler marks youngest British Columbian to die related to COVID-19

Child one of eight people to die from virus this weekend

Chakalaka Bar & Grill remains open in defiance of orders from Island Health to close. (Cole Schisler photo)
B.C. health authority seeks injunction against restaurant defying COVID-19 orders

Chakalaka Bar and Grill plans to continue serving customers without public health compliance

Most Read