Nurse Venus Lucero administers the first Pfizer-BioNTech COVID-19 vaccine at the Ottawa Hospital to Jo-Anne Miner at a vaccination clinic, Tuesday December 15, 2020 in Ottawa. THE CANADIAN PRESS/Adrian Wyld

Nearly 1,000 extra doses of COVID-19 vaccines have been administered in Ottawa beyond what was officially received thanks to an occasional sixth dose in some vials.

On Monday, Ottawa Public Health reported that 26,337 COVID-19 vaccine shots had been administered in Ottawa, despite the city having only received 25,350 to date. A brief statement on its COVID-19 dashboard said that vaccine inventory is based on an expected supply of five doses per vial and that an additional sixth dose is sometimes successfully extracted and administered to clients.

In a statement to CTV News Ottawa, the Ottawa Hospital says it is following guidelines from the province and Pfizer when administering vaccines.

"The Ottawa Hospital, like other vaccination clinics throughout Ontario, is following the directives from the Ministry of Health and Pfizer. At least five doses are extracted from every vaccine vial; if a full sixth vaccine dose can be extracted from a vial, that dose is used following normal vaccination procedures," the statement says.

The sixth dose was the subject of confusion last week when federal officials in charge of Canada's COVID-19 vaccine procurement said Pfizer's delivery calculations were based on having six doses per vial, whereas Canada's calculations were based on five doses per vial.

Health Canada is reviewing a formal request to change the label on the Pfizer BioNTech vaccines to reflect a sixth dose. Extracting that sixth dose is made easier using a particular size of syringe, 1cc, but it is in short supply in Canada. The more common 3cc syringe can be used to get a sixth dose out of the vial, but experts say it takes a higher level of skill to successfully extract it each time.

The Ottawa Hospital told CTV News there are no supply issues with syringes, locally.

"We do not have any concerns about supply of syringes for the COVID-19 vaccines, and are working with government partners to maintain supply," a statement said.

Around 400 Ottawa paramedics who have been vaccinating residents in long-term care homes have received COVID-19 vaccinations thanks to some of these additional doses.

Over the weekend, Paramedic Chief Pierre Poirier told CTV News Ottawa that when a sixth dose is successfully extracted, there is only a short time in which to use it.

"Whenever there is a sixth dose, that sixth dose is on the clock that it has to be used within a certain time limit. As we've gone through a home, we may end up with two or 10 or 15 extra doses because we've been able to draw a sixth dose out," said Poirier. "We've given that to staff, but we've also given that to paramedics on scene because the clock is ticking, we wouldn't want to waste a dose. We've had a number of paramedics to get vaccinated their first dose."

Ottawa Public Health will deliver an update at a press conference at 3:15 p.m. Tuesday.