BRUSSELS, Oct 18 (Reuters) - More than a billion COVID-19 vaccines produced in the European Union have been exported since December 2020, making the bloc the biggest exporter of the shots, European Commission head Ursula von der Leyen said on Monday. The vaccines had gone to more than 150 countries, and the EU had exported as many doses as it had distributed to its own citizens, von der Leyen added in a statement. The bloc started exporting vaccines at the start of the global roll out at a time when other major producers such as the United States were building up their own supplies and restricting exports. Most EU exports have been directed to bigger economies, including Japan, Turkey and Britain, who had contracts with vaccine makers based in the bloc. European Commission President Ursula von der Leyen gives a media statement on the coronavirus disease (COVID-19) vaccines, in Brussels, Belgium October 18, 2021. REUTERS/Yves Herman/Pool A woman holds a small bottle labelled with a "Coronavirus COVID-19 Vaccine" sticker and a medical syringe in this illustration taken October 30, 2020. REUTERS/Dado Ruvic European Commission President Ursula von der Leyen gives a media statement on the coronavirus disease (COVID-19) vaccines, in Brussels, Belgium October 18, 2021. REUTERS/Yves Herman/Pool 1/3 A woman holds a small bottle labelled with a "Coronavirus COVID-19 Vaccine" sticker and a medical syringe in this illustration taken October 30, 2020. REUTERS/Dado Ruvic Sales and donations to poorer nations have so far made up a small proportion of total exports, but the bloc was planning to distribute at least 500 million shots to the most vulnerable countries in coming months, von der Leyen said. Half of these doses would be supplied from a new contract that the EU wants to have with a producer of messenger RNA vaccines, officials said. The other half will be donations from EU states who have already bought vaccines. The bloc has already signed supply contracts with mRNA vaccine makers Pfizer-BioNTech (PFE.N), (22UAy.DE) for a total of up to 2.4 billion doses until 2023 and with Moderna (MRNA.O) for up to 460 million doses. The EU set up a vaccine export control mechanism in late January to monitor the outbound flow of shots from the continent. Although the mechanism allows the EU to block exports in the event of insufficient domestic supplies, it has been activated only once to prevent the shipment of 250,000 AstraZeneca (AZN.L) vaccines to Australia in March at the height of a dispute with the Anglo-Swedish firm about its supplies to the EU.