The EU has announced a deal with Pfizer-BioNTech for up to 1.8 billion extra doses of their Covid-19 vaccine.
The contract, on top of the 600 million Pfizer-BioNTech doses the commission has already secured, aims to supply the bloc with enough vaccines for booster shots, the European Commission said on Saturday.
Commission chief Ursula von der Leyen has promised more contracts will follow.
"Happy to announce that @EU Commission has just approved a contract for guaranteed 900 million doses (+900 million options) with BioNTech/Pfizer for 2021-2023," she tweeted from an EU summit in Portugal.
"Other contracts and other vaccine technologies will follow."
The EU said it could also expand vaccinations to minors and for exports to lower-income countries outside the bloc.
BioNTech of Germany and Pfizer of the US have stepped up supply to Europe with their jointly produced doses. Their vaccine is currently the main one being used in the EU.
After a slow start, the EU's vaccination drive has picked up speed, with more than a quarter of its population having received at least one injection.
The 27-nation bloc is on track to have 70 per cent of adults fully vaccinated by late July, and is already cautiously reopening ahead of its vital summer holiday period.
Ms von der Leyen has stood by the EU strategy of her commission being responsible for negotiating vaccine contracts for all member countries, despite early criticism that the process was too slow.
Europe is now debating with the US over whether lifting patents on Covid vaccines could boost supplies to poorer countries.
On Saturday, EU chief Charles Michel said the bloc was ready to discuss a US proposal of lifting patents on Covid-19 vaccines, although they were awaiting more detail from the US side.
"We are ready to engage on this topic, as soon as a concrete proposal would be put on the table," Mr Michel said.
The EU has so far sent more than 200 million doses to non-EU countries, while the US has sent only 2.7 million to Mexico in what it describes as a "loan".
The head of the World Health Organisation, Tedros Adhanom Ghebreyesus, tweeted that "Europe's role in the world is more critical today than ever as we fight Covid-19", adding that it "shows when we collaborate on common causes we are stronger together".
The EU is a major contributor to Covax, a WHO-backed scheme designed to provide doses to mainly lower-income countries.
