OTTAWA -- Health Canada has issued a label change authorization for the Pfizer-BioNTech COVID-19 vaccine, allowing administrators to draw one more dose from each vial than previously advised.

That means that going forward Canadian health-care professionals who are giving the shots will be able to extract six rather than five doses per vial, an update from what was authorized when the vaccine was first given the green light in December 2020.

This comes after a scientific review done by the agency of data submitted by Pfizer, demonstrating that six doses could safely and accurately be extracted from each vial.

Health Canada’s concern, in part, was based on a requirement to have a certain amount of “overfill” in each vial to ensure that there is enough vaccine to sufficiently draw up the accurate amount to yield the expected doses. The regulator’s review found that an “acceptable” amount remains in the vials once six doses are extracted.

“In order to extract a sixth dose reliably and consistently, a specialized syringe should be used. A low dead-volume syringe is designed to have a lower volume of liquid that stays in the hub of the syringe after the vaccine is administered. This minimizes the loss of vaccine volume per vaccination,” said Health Canada Senior Medical Adviser Dr. Supriya Sharma at a briefing on Tuesday.

Low-dead volume syringes are designed to have less liquid remaining in the hub of the syringe after the vaccine is administered.

The government says that while this new guidance comes into effect immediately, this week’s shipments will remain calculated at five doses per vial, but going forward the shipment allocations across Canada will be altered to reflect that there are six doses contained within each vial sent.

“This week, tens of thousands of Pfizer vaccine doses will be delivered to Canada. This is good news for so many people who will get a dose,” said Prime Minister Justin Trudeau at his Rideau Cottage address.

Conservative Leader Erin O’Toole is critical of the decision, saying it’s “mandating that the provinces do more with less.”

“The Liberals must also be clear with Canadians about whether Pfizer will replace any lost doses if the provinces are unable to extract the sixth dose,” he said in a statement.

Canada has a contract with Pfizer to receive 40 million doses of the vaccine, four million of which are to be delivered by the end of March. After weeks of shortages, next week’s shipment and those in the weeks ahead are set to increase considerably.

By counting the sixth dose what was set to be a shipment of approximately 335,000 doses is now being considered a shipment of around 400,000 shots. Similarly, the delivery coming in the last week of February will now include approximately 475,000 doses, rather than the 395,000 doses announced last week.

“While there is a change in doses contained in each vial, the country’s overall allotment from the manufacturer remains the same,” Maj.-Gen. Dany Fortin said Tuesday.

Fortin said that there are enough low-dead volume syringes in stock to continue Canada’s vaccine rollout under this new guidance, and more have been ordered and will continue to arrive over the next few months.

The goal is that with consistent use of these kinds of syringes, the instances in which health professionals are not reliably able to draw up six full doses will be lessened.

“We will continue to monitor it,” Sharma said, noting she has “anecdotally” heard of instances in which up to seven doses are able to be extracted from Pfizer vials.

American and European health authorities have already allowed the extraction of six Pfizer doses per vial.

The pharmaceutical giant is required to assist in Canada’s rollout of this change, including informing Health Canada quarterly of any issues reported from vaccine sites having issues extracting a sixth dose.