Nova Scotia's chief public health officer is asking doctors to return their stock of flu vaccine from last season.
Robert Strang says at least one person in the province has already been given last year's swine flu vaccine. He said that's not dangerous, but this year's flu shot is updated to include other strains.
The licence for last year's swine flu vaccine has expired.
Strang says this is the third time Nova Scotia doctors have been asked to return their leftover stock. Most have done so, he said, but some have not.
"Unfortunately, we still had some out there, and it was used," said Strang.
CBC News obtained a copy of a memo sent to doctors across the province explaining that last year's vaccine was accidentally given during this flu season and urging doctors to return supplies of the old vaccine by the end of the week.
"It was actually read out by one of the physicians in the clinic, and we all kind of raised our eyebrows, and we couldn't imagine that happening," said Dr. Michael Power of the Lacewood Medical Centre in Halifax.
Strang said people who are concerned about what shot they have received or will receive should talk to their doctor.
"It's not a safety issue in terns of getting an unsafe product, but if you thought you were getting the vaccine that's going to protect you against circulating seasonal flu strains this year and you got H1N1 vaccine, you're not going to be protected," said Strang..
This is the first year the province will be covering the cost of the seasonal flu vaccine for all Nova Scotians.