TORONTO -- As Ontario rolls out COVID-19 booster shots, some pharmacies are reporting that people are walking out after being informed that they would be receiving the Moderna vaccine rather than Pfizer's.

Justin Bates, who is the CEO of the Ontario Pharmacists Association, says he's hearing from pharmacies that around half of people are refusing to take Moderna.

"I think there's a lot of education that pharmacists have to do in other health care providers to demonstrate that (Moderna) is equal to Pfizer. It's safe, it's effective," he told CTV News on Friday.

The Moderna refusal can be mostly attributed to Pfizer-vaccinated people hesitant about mixing vaccine brands, Bates says. In spring of 2021, when most Canadians were starting to get their first and second doses, Moderna was having issues with supply. During that period, most people were vaccinated with Pfizer.

"When you get a flu shot, most people … wouldn't know who the brand manufacturer is. So, we got stuck on these names rather than understanding that an mRNA vaccine equals an mRNA vaccine," Bates said.

Pharmacies have also been prioritizing their supply of Pfizer shots for those under 30 years of age. Although Health Canada approved the Moderna booster for all adults 18 or older, the National Advisory Committee on Immunization (NACI) is only recommending Moderna for those aged 30 and up. NACI says in younger people, the Pfizer booster results in slightly lower rates of myocarditis, a rare side-effect of mRNA vaccines that causes heart inflammation.

"We want to make sure that we follow those guidelines and we are shifting most of the supply in the pharmacy channel over the next two weeks to Moderna," said Bates.

Bates is urging Ontarians to avoid vaccine shopping and instead get any vaccine booster as early as possible.

"Getting a vaccine now versus waiting or vaccine shopping is much more effective at providing the greatest and maximum immunity against Omicron," he said. "We keep encouraging people to essentially ignore the brands and get the vaccine that available to you, when it's available."