Pfizer and BioNTech will cut back on how many vials of COVID-19 vaccine they send Canada this year if the federal health regulator agrees to change the vaccine label to say every vial contains six doses instead of five.Medical professionals in the United States were first to discover in December that they could get six doses from each vial by using special syringes that trap less vaccine around the needle after an injection.Initially heralded as a way to stretch the precious vaccine even further, the company stepped in to note its contracts are for doses, not vials: If a recipient can get six doses instead of five, then Pfizer and BioNTech can ship fewer vials and still fulfil their contractual obligation.