TORONTO -- Ontario pharmacists say thousands of doses of the Moderna COVID-19 vaccine are set to expire soon and they warn the supply could go to waste if people don't show up to get a shot.

The CEO of the Ontario Pharmacists Association said some Moderna shots are set to expire in early August, and generally, supply that arrives in bulk must be used up within 30 days.

Justin Bates said a slowdown in Ontario's vaccine rollout and the public's preference for the Pfizer-BioNTech shot have made it difficult for pharmacists to use up the Moderna doses.

"It's an awful situation for them (pharmacists) to be in," Bates said in an interview. "They've done everything they can to make sure there's no wastage, but yet they're coming to that place where they may have to, or have already."

Bates' comments came after a health unit covering London, Ont., asked the public to roll up their sleeves for Moderna vaccines before more than 21,300 unallocated doses expire in two weeks' time.

Pharmacies are now ordering vaccine based on scheduled appointments to cut down on possible waste, said Bates, but they still need to use the supply they have on hand.

"The next couple of weeks (are) critical," he said. "It's complicated because you have any number of scenarios that could waste the vaccine."

On top of the expiration issue, Bates said it's also been challenging for pharmacists to use up the larger dose quantities that come in Moderna vials currently being supplied in Ontario.

Vials include enough vaccine for 14 shots and once a vial is punctured, all the vaccine must be used within 12 hours. If a patient cancels their appointment for a Moderna shot, it can't be filled by the end of the day, said Bates.

The problem is not limited to pharmacies.

The Middlesex-London Health Unit recently issued a call for residents to take the Moderna vaccine because it had thawed more than 21,300 doses of the shot that need to be used by Aug. 12.

In a statement, the health unit said vaccinations had declined over the previous weeks and the thawed shots were "above and beyond" appointments already allocated for second doses.

"We don't want this vaccine to go to waste, so we are asking people who aren't fully vaccinated to join us in the fight against COVID-19 and consider receiving a first or second dose of Moderna," Dr. Chris Mackie, the region's top doctor, said earlier this week. The health unit also stressed that the Pfizer-BioNTech and Moderna shots can be used as first and second doses safely.

A spokeswoman for the health minister said the province is working with the Middlesex-London Health Unit to help reallocate doses to areas of need.

"Public health units are working to keep vaccine wastage to a minimum and are encouraging walk-ins where appropriate," Alexandra Hilkene said.

"We are also working with federal partners to explore vaccine donation opportunities in the future."

Bates said his organization wants a provincewide program to help redirect doses at risk of being wasted to another site more likely to use them, though he noted that process would be complicated.

This report by The Canadian Press was first published August 1, 2021.