TORONTO -- Six people in Vaughan, Ont. were injected with saline when they were supposed to be getting the COVID-19 vaccine, health officials say.

Mackenzie Health said the six people were injected with saline, which is used to dilute the COVID-19 vaccine prior to use, on March 28.

"Saline injection does not cause any harm, however this should not have happened,” Mackenzie Health said in a statement posted online Monday.

"Our internal quality assurance processes allowed us to identify this issue in a timely manner and contact the impacted individuals to disclose the issue."

Mackenzie Health said they “sincerely apologize for error” and have undertaken a full review of their processes to ensure it doesn’t happen again.

Officials did not say which clinic the six patients visited.