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

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.

Tala MacDonald, a 17-year-old student at Mount Sentinel Secondary who is also a volunteer firefighter, has won the $100,000 Loran Scholarship. Photo: Submitted
West Kootenay student wins $100K scholarship

Tala MacDonald is one of 30 Canadians to receive the Loran Scholarship

Kristian Camero and Jessica Wood, seen here, co-own The Black Cauldron with Stephen Barton. The new Nelson restaurant opened earlier this month while indoor dining is restricted by the province. Photo: Tyler Harper
A restaurant opens in Nelson, and no one is allowed inside

The Black Cauldron opened while indoor dining is restricted in B.C.

First-year Selkirk College student Terra-Mae Box is one of many talented writers who will read their work at the Black Bear Review’s annual (virtual) launch on April 22. Photo: Submitted
Interior Health nurses administer Pfizer-BioNTech COVID-19 vaccines to seniors and care aids in Kelowna on Tuesday, March 16. (Phil McLachlan/Kelowna Capital News)
69 new cases of COVID-19 in Interior Health

The total number of cases in the region is now at 9,840 since the pandemic began

Jake the service dog is trained to give calming hugs to his caretaker and handler, Rae-Lynee Dicks, who lives with post-traumatic stress disorder. Photo: Laurie Tritschler
Jake and Rae-Lynne: The story of a Grand Forks woman and her service dog

Jake is on his way to completing his training, but it’s been difficult to socialize him in the pandemic

A syringe is loaded with COVID-19 vaccine at a vaccination clinic run by Vancouver Coastal Health, in Richmond, B.C., Saturday, April 10, 2021. THE CANADIAN PRESS/Jonathan Hayward
B.C. to open up COVID vaccine registration to all B.C. residents 18+ in April

Registration does not equate to being able to book an appointment

(Black Press file photo).
Multiple stabbings at Vancouver Island bush party

Three youths hospitalized after an assault in Comox

Selina Robinson is shown in Coquitlam, B.C., on Friday November 17, 2017. British Columbia’s finance minister says her professional training as a family therapist helped her develop the New Democrat government’s first budget during the COVID-19 pandemic, which she will table Tuesday. THE CANADIAN PRESS/Darryl Dyck
B.C. finance minister to table historic pandemic-challenged deficit budget

Budget aims to take care of people during pandemic while preparing for post-COVID-19 recovery, Robinson said

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

Lord Tweedsmuir’s Tremmel States-Jones jumps a player and the goal line to score a touchdown against the Kelowna Owls in 2019. The face of high school football, along with a majority of other high school sports, could significantly change if a new governance proposal is passed at the B.C. School Sports AGM May 1. (Malin Jordan)
Power struggle: New governance model proposed for B.C. high school sports

Most commissions are against the new model, but B.C. School Sports (BCSS) and its board is in favour

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

B.C. homeowners are being urged to take steps to prepare for the possibility of a flood by moving equipment and other assets to higher ground. (J.R. Rardon)
‘Entire province faces risk’: B.C. citizens urged to prepare for above-average spring flooding

Larger-than-normal melting snowpack poses a threat to the province as warmer weather touches down

Vancouver-based Doubleview Gold Corp. is developing claims in an area north of Telegraph Creek that occupies an important place in Tahltan oral histories, said Chad Norman Day, president of the Tahltan Central Government. (THE CANADIAN PRESS/HO)
B.C. Indigenous nation opposes mineral exploration in culturally sensitive area

There’s “no way” the Tahltan would ever support a mine there, says Chad Norman Day, president of its central government

Most Read