The European Union has secured 200 million more doses of the Pfizer/BioNTech COVID-19 vaccine, with an option to buy 100 million additional doses, bringing the total number of potential doses contracted for to 600 million.

The European Commission, which is negotiating advance orders of the vaccine on behalf of the EU’s 27 members states, said the additional doses will be delivered starting in the second quarter of the year. The vaccine has received a conditional marketing authorization in the EU and is now being administered to high-risk groups in the member states.

The commission, which has also given a conditional marketing authorization to the Moderna vaccine, says it “has secured up to 2.3 billion doses from the most promising vaccine candidates” and that any excess will be distributed to neighboring countries outside the EU bloc.