Seventy-one members of the Chippewas of Saugeen First Nation in Ontario were given expired COVID-19 doses for a month before they were told of the error earlier this week.
In a two-minute briefing Friday afternoon, Indigenous Services Canada (ISC), which administered the expired Pfizer-BioNTech doses in error between Aug. 13 and Sept. 9 in the Georgian Bay community, said it was working on a plan to "customize the approach to reimmunization" for those affected.
Dr. Tom Wong, executive director and chief medical officer of public health for ISC, spoke in the briefing.
But officials refused to answer questions from reporters, saying only they were working with local health authorities before disconnecting from the virtual briefing.
Wong did not say how many of the 71 community members the ISC has managed to reach.
It took the agency a week to tell people in the community they'd been given the expired doses, an error for which the department "sincerely apologizes," ISC wrote in a letter to the community Thursday.
The department sincerely apologizes for the vaccine error and the concern that it may cause for the members of Saugeen First Nation - Indigenous Services Canada
The Pfizer-BioNTech doses expired on Aug. 9, but were administered to community members between Aug. 13 and Sept. 9, according to a letter from ISC that was sent to the First Nation.
"While receiving a vaccine that is beyond its best-before date does not pose health risks to the individual, the recommendation is for the individual to be re-vaccinated," ISC wrote in the letter.
"The department sincerely apologizes for the vaccine error and the concern that it may cause for the members of Saugeen First Nation."
Vaccines can lose their strength if given after their best-before date, officials have said, and may make them less effective in protecting people from the COVID-19 virus.
Wong said the timing of the re-vaccination will depend on when a person received their dose and how close it was to the expiration date.
The error also means those who have been given their shots are not considered fully immunized and won't be able to access places such as restaurants or other venues where Ontario's vaccine passport is needed.
There are questions about why it took a week to tell the community about the error. ISC learned of the issue on Sept. 15; the community was told about it Sept. 22.
"We had to confirm the facts and determine what actually happened," Robert Rice, communications officer for Saugeen First Nation, wrote to the community. "We were waiting on direction from the vaccine manufacturer. We also had to co-ordinate with the Grey Bruce Public Health Unit, which is where we get the vaccine from.
"We did immediately reach out to the health director, band manager, COVID-19 safety lead in community and the chief."
How the error happened
Saugeen First Nation received its vaccine shipment on July 13. The expiration date on the vials said October 2021, but is only correct if the vaccine remains frozen.
When thawed and stored, Pfizer-BioNTech is only good for 31 days, while Moderna vaccines are good for 30 days. The vaccines at Saugeen First Nation, therefore, expired on Aug. 9, and while that was noted on a box, it was not written on the vials themselves.
"While administering the vaccine, [Indigenous Services Canada] nurses checked the expiry date on the vial and not on the box," the First Nation wrote in a separate letter to the community.
ISC said in an email to CBC News on Friday that it "recognizes the significant concern that this may cause to the community" and has launched an internal investigation.
"ISC also contacted the vaccine manufacturer, Pfizer, Public Health Ontario and other Provincial departments seeking guidance on next steps," said ISC spokesperson Leslie Michelson.
CBC News has reached out to Saugeen First Nation Chief Lester Anoquot, and will update the story when any responses are received.