TORONTO -- Like many students eyeing in-class learning this fall, Nyle Maker is on the hunt for his second dose of Pfizer's COVID-19 vaccine before starting university in Hamilton.

But unlike most, the 18-year-old McMaster University student has already received a full series of the Russian vaccine Sputnik V in his home country of Pakistan and is embarking down a murky road of not just mixing shots, but effectively doubling them.

Maker says he was led to believe he didn't meet the vaccine requirements to secure a room under McMaster's shifting campus housing policy, because Sputnik hasn't received the rubber stamp from Health Canada or the World Health Organization.

The university recently revised its rules to give international students a little more leeway, but these changes were too little and too late to help Maker.

By the time he had one dose of Pfizer under his belt, Maker says McMaster's residences had filled up, leaving him and many other students on a waiting list.

"My biggest concern for when I arrive in Canada is my accommodation," says Maker.

"Renting a house (or) flat from abroad is really difficult, so I will have to do that when I get there."

Many universities and colleges have issued vaccine mandates to live or learn on campus, creating extra layers of complication and confusion for many would-be students from abroad.

McMaster University, University of Toronto and Western University in London are among the post-secondary institutions requiring that students -- international and domestic -- have at least one dose of a WHO-authorized vaccine to move into residence.

The universities say they'll give residents a grace period to comply with the requirements, and help young newcomers get their jabs in Canada.

Toronto's Seneca College goes further with its mandate, insisting all students and staff be vaccinated before setting foot on campus Sept. 7. Otherwise, there is online instruction.

The four schools say they accept the World Health Organization's list of vaccines approved for emergency use, which include formulations by Chinese companies Sinovac Biotech and Sinopharm in addition to the Health Canada-authorized Pfizer-BioNTech, Moderna, Oxford-AstraZeneca and Johnson & Johnson products.

But that leaves out Covaxin, made by Bharat Biotech in India, a top source country of international students at Canadian universities, and Russia's Sputnik V vaccine, used in dozens of countries including South Korea, Argentina and the United Arab Emirates.

Ontario's health ministry advises individuals who have received non-WHO-approved vaccines be offered an additional series of Health Canada-authorized jabs.

However, the ministry acknowledges there's no data to support the safety or efficacy of this approach.

The Public Health Agency of Canada says it's assessing the issue.

Dr. Zain Chagla, an infectious disease expert with McMaster University, sees the rationale behind making vaccination a condition for on-campus residence, which can be a "breeding ground" for contagion.

But he said there's not a lot of science on the impacts of mixing different vaccine products that use different technologies and have varying authorizations. Matters become murkier when it comes to giving people third or fourth doses.

"I don't suspect that giving another vaccine to people who have had one vaccine series is going to necessarily lead to any decrease in efficacy. If anything, it'll increase. But it's a data-free world," he said.

"We're counselling patients about what this means and what it looks like long-term for them, but we don't really have a great answer."

Immigration consultant Roya Golesorkhi said some of the international students she works with would rather not risk doubling up on vaccine varieties.

"It's a valid concern," said Golesorkhi. "They see themselves as fully vaccinated, and they don't want to get vaccinated again here."

The Canadian Federation of Students raised equity concerns for immunized international students who are forced to seek additional doses even as many of their home countries struggle to procure enough vaccines to inoculate their populations.

"Students feel that it is an unnecessary thing," said Bipin Kumar, the group's international student representative.

"When there is a huge vaccine shortage already across the world, they're being forced to get additional vaccines for just lack of recognition by (Canada's) health authorities."

This report by The Canadian Press was first published July 29, 2021.