Canada is considering allowing patients to receive two different types of COVID-19 vaccines as the country deals with shortages of shots from AstraZeneca Plc and Moderna Inc.

Federal health officials are closely watching a U.K.-based trial in which participants received two kinds of shots. Results are expected in the next month or so, Supriya Sharma, chief medical adviser at Health Canada, said Wednesday at a news conference.

Vaccine mixing “would most likely be an mRNA vaccine like a Pfizer or a Moderna, combined with an AstraZeneca which is a viral vector vaccine,” Sharma said. Canada has fully vaccinated just 2.6 per cent of its population, the second-lowest rate among Group of Seven countries, according to the Bloomberg Vaccine Tracker. It’s grappling with limited supplies of all but the Pfizer Inc.-BioNTech SE vaccine.

If adopted, the new protocol would mark another major deviation from original vaccine guidelines. Canada has opted to extend the length of time between mRNA vaccines from the recommended three to four weeks to as much as four months, in order to stretch supplies.

Health officials also approved the Pfizer vaccine for ages 12 to 15. That makes Canada the second country to allow use for adolescents, after Algeria, according to CBC News. Pfizer and its German partner released data in March from studies showing their vaccine is safe for that age group.

“This is wonderful news,” Christine Elliott, Ontario’s health minister, said in a separate news conference. The government of Canada’s largest province is expecting to receive an increased supply of the Pfizer and Moderna shots this month and is “actively working” on the timing for younger vaccinations, she said. Ontario has been under an emergency stay-at-home order for weeks because of a rising number of serious cases.

The province of Alberta said it will begin booking vaccine appointments for adolescents on May 10.

Canada’s vaccine roll-out has been plagued with confusion, amid conflicting information about safety and protocols for who can get the shots when.

The chair of an expert panel, the National Advisory Committee on Immunization, caused a furor this week when she suggested some lower-risk Canadians might be better off waiting for an mRNA vaccine.

“If, for instance, my sister was to get the AstraZeneca vaccine and die of a thrombosis when I know that it could have been prevented and she’s not in a high-risk area, I’m not sure I could live with it,” Caroline Quach-Thanh said in a television interview.

That forced Prime Minister Justin Trudeau to push back, urging Canadians publicly to take the first dose of whatever vaccine is available.

While NACI’s position was likely intended to provide nuance, it effectively countered weeks of efforts by health officials to overcome vaccine hesitancy and convince Canadians to ignore reports of rare blood clots associated with the AstraZeneca jab and take the first shot offered.

The size and timing of additional AstraZeneca shipments is unknown, partly because India, from which Canada procures some of its vaccine supply, is battling the world’s worst outbreak of the virus.

So far, Canada’s most reliable vaccine source has been Pfizer but supply has been tight enough to necessitate extending the gap between shots with very few exceptions, such as for those with certain types of cancer.

Even health-care workers treating the most critically ill COVID-19 patients are not permitted to have second doses until everyone has a chance at a first shot, a situation some say is skirting with disaster.

“Health-care workers are in such limited supply, everywhere across the country. Even if a relatively small amount were to get sick, it could have devastating consequences,” Michael Chu, chief of cardiac surgery at London Health Sciences Centre, said in an interview.

Most of Chu’s colleagues, including those treating critically ill COVID-19 patients, have only received one dose, typically of Pfizer or Moderna, he said. Getting a second shot is becoming more urgent. “Everyone is exhausted, they’re burning out, and they just want to be protected.”

Hospitals have been reluctant to release information about infections among doctors or nurses who received only one shot, citing privacy concerns, but it’s known that infection is still possible after only one dose. And while -- fortuitously -- it now appears a greater-than-recommended delay between AstraZeneca doses may make that vaccine more effective, the impact on Pfizer’s efficacy is less clear.

As recently as March 23, Pfizer cautioned that there were no data to support extending the window for doses beyond 21 days. For Chu, not only does that mean staff are at risk as they wait for their second shot, but they may not get optimal protection afterward.

“There is really very little evidence to show we’re going to receive sufficient protection with this delay,” he said. “Health-care workers are risking their lives and it’s not like general exposure; it’s coming to work every day to treat COVID-positive patients. They deserve to have the best protection available to them.”