MONTREAL -- The daughter of a 97-year-old woman in Montreal was happy when her mother received the Moderna COVID-19 vaccination but was shocked and confused when she got a Pfizer vaccine as well.

Patrizia Di Biase said that her mother Antonietta Pollice received the Moderna vaccine Jan. 7 at 11 a.m. at the Maison Herron long-term care facility.

Pollice has dementia and left the residence four days later and was transferred temporarily to the CHSLD Joseph-Francois-Perrault while she waits for a permanent spot at the CHSLD Dante.

It was at her temporary home that Pollice received the Pfizer vaccine on Jan. 22, Di Biase said, who was notified of the mix up when a nurse at Joseph-Francois Perrault called to apologize.

"I got a call saying we're really sorry, but we gave her the vaccine by mistake and it was the Pfizer," said Di Biase. "I said what do you mean you gave it to her by mistake? I said it's on her file and I also got a call the week before asking if she can get the vaccine and I said, 'no she can't because she's already gotten the Moderna."

On its website, Health Canada says no data exists on the effects, positive or negative, of mixing the vaccines, an opinion echoed by cardiologist Christopher Labos. 

"Maybe these vaccines are interchangeable, maybe they're not," he said. "The reality is, we just don't know. No one has tested them. Nobody has done a study looking at what happens if you get dose one from Pfizer and dose two from Moderna or vice versa."

Patients' rights advocate Paul Brunet said lax communication has been a recurring problem during the pandemic.

"I have so many complaints of a lack of communication, a total black out in terms of communication," he said. "People who hear their relative has died during the first wave of COVID, without even knowing that the state of that person's health had degraded that much."

Di Biase feels staff should have had a list with who wanted the vaccine and who didn't.

"If they just went room-to-room, it means they didn't have a list," she said. "Right now, she's doing well, but we don't know further along. Check it twice. Make sure there's a consent."

The regional health authority in charge of CHSLD Joseph Francois Perrault said it's looking into the situation.