OTTAWA -- Canada's National Advisory Committee on Immunization (NACI) is not recommending the use of AstraZeneca’s COVID-19 vaccine in individuals aged 65 years and older, due to “the insufficiency of evidence of efficacy in this age group at this time.”

However, Health Canada stressed that "there were no safety concerns in this age group in the clinical studies, nor in the large numbers of seniors who have been vaccinated to date in countries that have already authorized the AstraZeneca vaccine and are administering it to people over 65 years of age."

NACI’s new guidance follow Friday’s Health Canada approval of the AstraZeneca vaccine (ChAdOx1-S), the first “viral vector” vaccine to be authorized in this country. Specifically, the agency has given the green light to two manufacturers to provide authorized AstraZeneca doses to Canada: one manufactured by AstraZeneca and developed in partnership with Oxford University, and another version developed by the Serum Institute of India and Verity Pharmaceuticals called COVISHIELD.

The two-dose vaccine was approved for use in people 18 years of age and older, including seniors. However, when Health Canada signed off on the new shot last week, it also had noted that of the available clinical trial data: “the results were too limited to allow a reliable estimate of vaccine efficacy in individuals 65 years of age and older.”

“Efficacy in this age group will be updated as additional data becomes available from currently ongoing trials,” said Health Canada.

On Monday, Alberta Health Minister Tyler Shandro said the provincial government would not give the Oxford-AstraZeneca vaccine to anyone over the age of 65.

"How that's going to change the administration of those who are in Phase 2 is still to be determined," he told reporters. "We'll be making those decisions and announcing them fairly soon."

Other countries have made the decision to not administer the AstraZeneca vaccine to people over the age of 65, citing the limited information about its efficacy, based on the small number of people over 65 that participated in clinical trials. Though on Monday, France announced it was easing its guidance, permitting people aged 65 and older to receive the vaccine.

Last week, Public Health Scotland, which has been administering the Oxford-AstraZeneca vaccine since Dec. 30, released a report indicating hospital admission due to COVID-19 fell 94 per cent after receiving the vaccine. Most of the 500,000 people involved in the study were over the age of 80.

Health Canada officials said last week that blood tests showed people over 65 still produced COVID-19 antibodies after vaccination and the "real world" evidence in countries that have been using the AstraZeneca vaccine showed no safety concerns in seniors.

“Health Canada has rigorously evaluated the data available from AstraZeneca clinical trials and determined that this vaccine is safe to be administered in people over 65 years of age and older,” the agency said in a statement on Monday.

“There are now encouraging reports that real world use in older populations may already be showing benefits with respect to outcomes of interest, such as hospitalization,” the statement added.

“It's not to say that it doesn't work, it's that we're not sure. It's less convincing,” said University of Toronto epidemiologist Colin Furness in an interview on CTV News Channel.

NACI’s advice are recommendations and not rules, allowing provinces to continue to tailor their vaccination rollout campaigns to fit the pandemic reality in each region and determine which demographics are best suited to receive which vaccine based on the number of doses available.

Health Canada has said that the efficacy of the vaccine was estimated to be 62.1 per cent in people ages 18 to 64, with the second shot being administered between four and 12 weeks after the first.

In new guidance issued Monday NACI— the advisory committee offering national advice on Canada’s COVID-19 vaccination strategy—also recommends the two doses of this vaccine should be given the full 12 weeks apart.

“A 12-week interval is preferred for the AstraZeneca COVID-19 vaccine based on vaccine principles, feasibility considerations for pandemic supply management, and available ad hoc analyses of clinical trial interval data from the manufacturer,” NACI states in the updated guidance.

The AstraZeneca vaccine is logistically easier to administer than the Pfizer or Moderna doses as it can be shipped and stored in fridges rather than freezers. This potentially opens up where and to who it can be administered, with provinces beginning to expand their immunization campaigns. However, it remains to be seen how this new guidance will impact the national rollout and administration of these doses, with the initial shipment of vials potentially arriving within days.

“I don't think it changes a lot in the picture because we could absolutely you know, give this vaccine to people who are under the age of 65. It is my full expectation that the vaccine will be safe and effective for people over the age of 65 to probably 85 or so,” Dr. Hassan Masri, an ICU physician and associate professor at the University of Saskatchewan, said Wednesday on CTV News Channel, adding that in the meantime people aged 65 and over could be prioritized to receive either the Moderna or Pfizer shots.

Procurement Minister Anita Anand’s office has not confirmed the timing of the first delivery of these newly-approved doses, or how many shots will be sent to Canada to start, but in total Canada is set to receive 23.9 million doses of the AstraZeneca vaccine.

The majority of these doses—20 million from the AstraZeneca/Oxford agreement—are set to land in Canada from the U.S. starting in April, but the first 500,000 shots of a separate two-million dose deal with the Serum Institute and Verity Pharmaceuticals, are expected by the end of March.

In an email to CTV News, a spokesperson for Verity Pharmaceuticals said that a delivery is expected to arrive in Canada “mid-week” this week. The delivery of the remaining 1.9 million AstraZeneca doses is coming through the COVAX initiative, though the timeline for those doses landing in this country has yet to be established.

With files from The Canadian Press