OTTAWA -- As some provinces begin expanding eligibility for the AstraZeneca COVID-19 vaccine, the National Advisory Committee on Immunization (NACI) was set to release updated guidance about the usage of the two-dose viral vector injection on Tuesday but has now postponed its announcement “in order to further validate its data analysis.”

In a statement to CTV News, Public Health Agency of Canada spokesperson Eric Morrissette said that NACI “expects to be able to release its finalized guidance later this week.”

Members of the advisory group focused on issuing recommendations on the use of vaccines in Canada were to be joined by federal and provincial officials for a briefing on NACI’s AstraZeneca “evidence summary update,” following a meeting on the topic last week.

While Health Canada has authorized the AstraZeneca vaccine for use in Canadians aged 18 and over, in late March, reacting to concerns over the rare risk of blood clots, NACI issued guidance recommending that the vaccine only be used in adults 55 years of age and older.

This advice was swiftly adopted by provinces, but with reports of AstraZeneca doses sitting unused on pharmacy shelves, Ontario, Alberta, British Columbia, and Manitoba have in recent days moved to lower the eligibility age to 40, allowing younger adults to book appointments.

Still, Canada’s supply of AstraZeneca doses remains sparse, with just 2.3 million total doses distributed across Canada as of April 14. These shots have come through smaller deals Canada made to get doses from COVAX, India, and the United States, rather than from the main contract with AstraZeneca-Oxford.

Procurement Minister Anita Anand has said that, by the end of June, a total of 4.1 million AstraZeneca shots are expected to arrive in Canada, with the bulk of deliveries set to come sometime between July and September.

Should NACI come forward later this week and advise that Canada broaden the eligibility, it would still be up to each province and territory to determine how it wants to prioritize access to the current supply. So far, just three cases of vaccine-induced prothrombotic immune thrombocytopenia have been reported in Canada following receiving an AstraZeneca dose, and all three people are recovering.

NACI’s current guidance to limit the shot to those 55 and older was not the first time the committee has suggested limiting the use of this vaccine. Previously NACI had recommended that Canadians 65 and older receive prioritized access to the Pfizer-BioNTech and Moderna shots due to the limited efficacy data of the AstraZeneca vaccine in older populations.

Over the course of NACI’s evolving advice, Health Canada has maintained that the AstraZeneca vaccine is safe and effective, and that any potential risks are greatly outweighed by the benefits of being immunized against COVID-19.

Earlier on Tuesday, Prime Minister Justin Trudeau met virtually with pharmacists across the country to talk about the state of the COVID-19 vaccine rollout, and thanked them for helping get shots into arms.

He and Deputy Prime Minister Chrystia Freeland said Tuesday that they are working to book vaccine appointments, now that they are eligible for the AstraZeneca shot in Ontario.

“I look forward to having a pharmacist give me my vaccine as soon as we can secure an appointment,” Trudeau said.

NACI has yet to issue any guidance around the use of the single-shot Johnson & Johnson vaccine, which Health Canada has also approved for use in anyone 18 years of age and older. The first shipment of 300,000 doses is expected to be delivered the week of April 27, and be in provinces and ready to administer in early May.