Six people in Vaughan, Ontario were mistakenly injected with saline instead of a COVID-19 vaccine, say health officials.

The incident occured on March 28 at the Mackenzie Health COVID-19 Vaccine Clinic, which is located at Cortellucci Vaughan Hospital, according to a statement issued Monday by Mackenzie Health.

“Saline is used to dilute the COVID-19 vaccine prior to administration. Receiving a saline injection does not cause any harm, however this should not have happened,” the statement said.

The clinic’s “internal quality assurance processes” allowed them to identify the issue “in a timely manner,” and the affected individuals were contacted and offered support, according to the statement.

Recipients who attended the clinic on March 28 were also informed that they will require an antibody test to detect if they received the Pfizer vaccine or will require another shot.

“We sincerely apologize for the error and for the uncertainty and concern this situation has caused,” Mackenzie Health said.

“We have undertaken a full review of our processes and have implemented additional safeguards to prevent this from happening again.”