Europe's medicines regulator gave the go ahead on Friday for an extra sixth dose to be extracted from Pfizer-BioNTech COVID-19 vaccine vials, increasing the number of available shots at a time when supplies are short.

EU countries started inoculating people with the Pfizer-BioNTech vaccine two weeks ago, after the European Medicines Agency (EMA) recommended the shot's conditional approval under an authorisation which allows five doses to be extracted from each vial.

"EMA's human medicines committee (CHMP) has recommended updating the product information for Comirnaty to clarify that each vial contains six doses of the vaccine," EMA said.

The vaccine is branded as Comirnaty in the EU.

Reuters had reported on Wednesday that the regulator was close to green lighting the move.

This change in authorisation could allow 20% more doses to be available in the EU under an existing contract with Pfizer, EU lawmaker Peter Liese had said.

To extract the sixth dose from a single vial, low dead volume syringes or needles, which only retain a low amount of solution after an injection, should be used, EMA said, adding that there should be no pooling from multiple vials to make up a full dose.