The EU's medicines watchdog said Friday that six doses of the Pfizer-BioNTech coronavirus jab can be extracted from each vial if the correct needles are used -- increasing the number of people who can be vaccinated with available supplies.  

The European Medicines Agency said that if low "dead-volume" syringes were used -- a specially-designed syringe that has less space between the needle and the plunger -- a sixth dose could be squeezed out of each vial of the vaccine.

"If standard syringes and needles are used, there may not be enough of the vaccine to extract a sixth dose from a vial," the EMA said in a statement.

The watchdog warned that if a full 0.3-millilitre dose is not left in the vial after the fifth dose, "the healthcare professional must discard the vial and its contents".

Healthcare workers should not mix the leftovers from "multiple vials to make up a full dose", it stressed.

The Amsterdam-based agency gave the green light on December 21 for the vaccine, developed by US pharmaceutical giant Pfizer and German company BioNTech, to be used in the 27-member European Union.

An additional dose from each vial could significantly accelerate the number of people being vaccinated each day in Europe, where numerous governments are facing accusations of a slow rollout. 

The new guidance from the EMA came as the EU struck a deal to double its previous supply of the Pfizer-BioNTech vaccine to 600 million doses. 

The EU has also approved the Moderna vaccine for use in member-countries, and the EMA indicated Friday that the bloc could approve a third vaccine developed by AstraZeneca before the end of January.