TORONTO -- Seventy-year-old Gordon Kroft just returned to Ontario from Miami—with a second shot of the Pfizer COVID-19 vaccine as his souvenir.

"It was easier than going to buy a loaf of bread," said Kroft, who walked into a Miami Walgreen's two weeks ago and rolled up his sleeve.

Kroft had received his first dose of the COVID-19 vaccine in Toronto in March, and was concerned about the risk of catching COVID-19 before getting his booster shot.

"I was just afraid to wait four more months for the second one," he said.

Kroft is among a growing number of Canadians who’ve been partially- or fully-vaccinated against COVID-19 abroad, including in the U.S. where demand for doses has slowed and many pharmacies do not require proof of citizenship for the vaccine.

But the Ontario government has no data on exactly how many people were immunized elsewhere, meaning the actual number of people with at least one dose of protection could be significantly higher than domestic data indicates.

"Those doses were obviously not inputted into the COVAX system, so those individuals really do need to connect with their local family physicians and make sure that they know that they have had the vaccine," Ontario Solicitor General Sylvia Jones said Wednesday.

"We want to include those people in our numbers," said Jones.

The province is calling on the federal government to implement a process to track Canadians who have been vaccinated outside of the country. The Ministry of Health said Wednesday that it will rely on proof of vaccination provided by the individual to support booking an appointment for a booster dose, if needed.

Canada is allowing a four-month dosing interval between shots, while the U.S. is permitting second doses to be administered three or four weeks after the first.

The land crossing between the two countries has been closed to non-essential trips since March 2020, and the American border agency confirmed Wednesday that it does not consider vaccination essential for entry purposes, meaning Canadians attempting to drive in for a COVID-19 shot could be turned away at the border.

Ontario’s latest domestic data indicate that 7,431,638 doses have been administered within the province, with 456,784 people fully vaccinated.