Some health authorities across the country have tossed out hundreds of doses of the swine flu vaccine because of miscalculations over how many of the time-sensitive doses are needed at community clinics.

Officials at some larger health districts, including Toronto and Halifax, say they have thrown out about one per cent of the total vaccine they've administered because of the doses' 24-hour shelf life.

In Toronto, that means close to 500 doses of the adjuvanted vaccine have been disposed of, even as people remain shut out of the priority groups entitled to receive the shot.

"We reconstitute as much vaccine as we think we're going to need, but sometimes our numbers are a wee bit off," said Ameeta Mathur, manager of the vaccine program for Toronto Public Health. "Once it's in the syringe from the vial and it's not used, we have to dispose of it."

The vaccine is reconstituted by mixing it with the adjuvant, an additive that boosts a person's response to the serum, and is then ready to be injected. But once mixed, the doses have to be used within 24 hours.

Mathur said there is little information on the stability of the vaccine once it has been reconstituted. Once the solution is drawn into a syringe, she said it can't be put back in the vial nor can the syringes be used the next day because of the lack of data on the vaccine's stability.

The Toronto health authority is using a ticket system for people lining up to get the vaccine, giving nurses an idea of how many doses to mix up through the day.

But Mathur said they sometimes get the numbers wrong and are stuck with vaccine they can't use.

Leftover doses sent to other clinics

In Nova Scotia, health workers in the province's largest district have thrown out about 80 doses because they have been unable to get them into peoples' arms before the vaccine hits the 24-hour expiry mark.

John Gillis, spokesman for the Capital District Health Authority, said they are trying to avoid discarding doses by shuttling them to other clinics where the shots are in short supply. But they are basing what they need in the run of a day from what they've seen previously and sometimes get it wrong.

"They can't be exactly right," he said. "They reach the end of the day and they've got some unused supply that won't make it to the next day."

Dr. Robert Strang, Nova Scotia's chief public health officer, said he understands it might be frustrating for groups still waiting to get immunized to hear that some of the vaccine is being discarded. But he said health officials are trying to keep waste to a minimum.

He said by giving it to doctors in group practices who can share it among their patients, they are hoping to "minimize the wastage."

A spokeswoman with the Department of Health in Newfoundland and Labrador said they haven't discarded any vaccine, while officials in New Brunswick and Nunavut said they also have no reports of discarded doses.

A Department of Health official in Alberta said he didn't have numbers on the level of waste, if any. Dr. Moira McKinnon, Saskatchewan's chief medical health officer, said they have not yet had any reports of vaccine being discarded, but that it is possible.

"We certainly haven't had any reports of wastage so far, but it may have occurred," she said. "The [health] regions are very conscientious about the use of this vaccine, and in fact in some areas they're managing by just careful use to get an extra dose out of some of the vials."