Why is Pfizer asking Canada to draw more vaccine doses from each vial?

Vaxx Populi: Canada’s contract with the pharmaceutical company for 40 million doses is based on five doses per vial. Pfizer wants it to be six.

The first page of the Canadian product monograph for the Pfizer-BioNTech COVID-19 vaccine, which explains precisely how this vaccine is to be used in the country, includes this line: “Multiple Dose Vial (after dilution each vial contains 5 doses of 0.3 mL).”

Like all such liquid vaccines, each Pfizer vial contains more than the precise amount to be administered, as there is necessary wastage, including as a result of the design of a regular syringe, which traps some vaccine inside it after the dose is administered. 

Normally that isn’t an issue. But right now, every drop of COVID-19 vaccine is precious. 

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And, as medical personnel around the world began using the new Pfizer vaccine, they discovered that they could often get a sixth dose from that five-dose vial. That amounts to 20 per cent increase in the number of doses, which was welcome news to Pfizer, currently trying to produce enough vaccine to meet worldwide demand (and their contract obligations.) (To avoid cross-contamination, a partial sixth dose from one vial is not permitted to be topped up from another vial.) 

Pfizer’s 40-million dose contract with Ottawa is based on five doses per vial. Pfizer wants it to be six. “In a situation of limited vaccine supply amidst a public health crisis, our intent with this label change is to provide clarity to health care providers, minimize vaccine wastage, and enable the most efficient use of the vaccine,” Christina Antoniou, director of corporate affairs for Pfizer Canada, told Global News. 

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The request, still pending with Health Canada, comes in the wake of other jurisdictions altering their contracts from five doses per vial to six doses. On Jan. 6, the United States amended its contract. Two days later, the European Union did the same.

But while such a change would allow Pfizer to fulfill its Canadian order with fewer vials, it also presents a problem for those actually administering the doses. Because in order to consistently extract that sixth dose, they need specialized low-volume or zero-dead space syringes, which are designed to leave very little excess vaccine in the syringe compared to regular syringes. 

And as countries around the world try to get more vaccine out of their vials, those specialized syringes are suddenly in short supply. The Hastings Prince Edward public health unit in Ontario even reached out to local veterinary clinics for syringes that were smaller than the ones it had, the Globe and Mail reported. Last week, the United States government concluded a deal with Pfizer by which it tracks the distribution of vaccine and the type of accompanying syringes within the country: regular syringes mean vials count for five doses, while six doses are counted if the vials are shipped with low-volume syringes, the Washington Post explained

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Most of the syringes on order for the COVID-19 vaccine program in Canada aren’t low-volume versions. The federal government recently has placed an order for 37.5 million of those crucial syringes. Next week, two million are arriving in Canada, confirmed Arianne Reza, assistant deputy minister of Public Service and Procurement Canada. Health Canada told Maclean’s that delivery of the rest of the order will continue until mid-April. 

But professionals are still concerned about the consistency with which a sixth dose can be extracted. “A sixth dose is not guaranteed,” cautioned Dr. Deena Hinshaw, Alberta’s chief medical officer of health, at a press conference on Jan. 28. 

“To achieve six doses per vial, a [low-volume] syringe must be used and, even then, we estimate that the sixth dose can only be achieved about 75 per cent of the time,” she said. (Using currently available syringes, Alberta public health immunizers have “have been able to safely extract a sixth dose from approximately half of the Pfizer vials,” Hinshaw said, a percentage in line with what she’s heard from other provinces.) Even Pfizer’s Antoniou told Global News that her firm does “not have information that shows how often six doses are extracted from vials.”

UPDATE: On Feb. 9, Health Canada granted Pfizer permission to change the number of doses extracted per vial of vaccine from five to six. 

As Canada rolls out the country’s most complex vaccination project to date, Maclean’s presents Vaxx Populi, an ongoing series in which Patricia Treble tackles the most pressing questions related to the new COVID-19 vaccines. Send us a question you’d like answered at If you have specific questions about your own health, we recommend consulting a family doctor or the local public health authority in your area.

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